feat: Add license attribution for all files

Signed-off-by: David Runge <dave@sleepmap.de>

book/source/01-intro.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Introducing OpenPGP
 
 This documentation project seeks to introduce OpenPGP concepts and functionalities to software developers who wish to use it in their projects.

book/source/02-highlevel.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # A high-level view
 
 ## Why OpenPGP?

book/source/03-cryptography.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 (cyrptography_chapter)=
 # Cryptographic concepts and terms
 

book/source/04-certificates.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 (certificates_chapter)=
 # Certificates
 

book/source/05-private.md

@@ -1,3 +1,8 @@
+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 (private_key_chapter)=
 # OpenPGP private keys
 

book/source/06-certifications.md

@@ -1,3 +1,8 @@
+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 (certifications_chapter)=
 
 # Certification signatures

book/source/07-signing_data.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 (signing_data)=
 # Signatures over data
 

book/source/08-signature_internals.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Signature "internals"
 
 ```{admonition} TODO

book/source/09-verification.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 (verification_chapter)=
 # Verification
 

book/source/10-encryption.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 (encryption_chapter)=
 # Encryption
 

book/source/11-decryption.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 (decryption_chapter)=
 # Decryption
 

book/source/12-compression.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Compression
 
 ## Zooming in: Packet structure

book/source/13-armor.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # ASCII Armor
 
 The native format of OpenPGP data is binary.

book/source/14-pitfalls.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Pitfalls / Things to keep in mind
 
 ## Key IDs are really not guaranteed to be unique

book/source/15-migration.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Migration from v4 to v6
 
 ```{admonition} TODO

book/source/16-policy.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Algorithms and Policy
 
 ```{admonition} TODO

book/source/17-zoom_certificates.md

@@ -1,3 +1,8 @@
+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Zooming in: Packet structure of certificates and keys
 
 Now that we've established these concepts, and the components that OpenPGP certificates consist of, let's look at the internal details of an example certificate.

book/source/18-zoom_private_keys.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Zooming in: Packet structure of private key material
 
 ## A look at Alice's (unencrypted) private key packets

book/source/19-zoom_signatures.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Zooming in: Packet structure of data signatures

book/source/20-zoom_encyption.md

@@ -1 +1,6 @@
+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Zooming in: Packet structure of encrypted data

book/source/21-resources.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # External resources
 
 [OpenPGP version 6 draft specification](https://datatracker.ietf.org/doc/draft-ietf-openpgp-crypto-refresh/) draft-ietf-openpgp-crypto-refresh [2023]

book/source/22-glossary.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Glossary
 
 ```{glossary}

book/source/23-acknowledgements.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Acknowledgements

book/source/a-artifacts.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # Appendix A: OpenPGP artifacts
 
 (alice_priv)=

book/source/conf.py

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+# SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+# SPDX-License-Identifier: CC0-1.0
+#
 # Configuration file for the Sphinx documentation builder.
 #
 # For the full list of built-in configuration values, see the documentation:
@@ -7,7 +10,7 @@
 # https://www.sphinx-doc.org/en/master/usage/configuration.html#project-information
 
 project = 'OpenPGP for application developers'
-copyright = '2023, The "Notes on OpenPGP" project'
+copyright = '2023, The "Notes on OpenPGP" project, CC-BY-SA-4.0'
 version = "0.01"
 
 # -- General configuration ---------------------------------------------------

book/source/index.md

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+<!--
+SPDX-FileCopyrightText: 2023 The "Notes on OpenPGP" project
+SPDX-License-Identifier: CC-BY-SA-4.0
+-->
+
 # OpenPGP for application developers
 
 **{sub-ref}`today`**