contributing: Link to CoC and add no-LLM statement

This is copied ad verbatum from libadwaita, which itself was
introduced based on [1].

[1]
https://discourse.gnome.org/t/loupe-no-longer-allows-generative-ai-contributions/27327

CONTRIBUTING.md

@@ -3,7 +3,25 @@
 When contributing to the development of GNOME Calendar, please first discuss the change you wish to
 make via issue, email, or any other method with the maintainers before making a change.
 
-Please note we have a code of conduct, please follow it in all your interactions with the project.
+## Code of Conduct
+
+When interacting with the project, the [GNOME Code of Conduct](https://conduct.gnome.org/) applies.
+
+## Use of Generative AI
+
+This project does not allow contributions generated by large languages models (LLMs) and chatbots.
+This ban includes tools like ChatGPT, Claude, Copilot, DeepSeek, and Devin AI. We are taking these
+steps as precaution due to the potential negative influence of AI generated content on quality, as
+well as likely copyright violations.
+
+This ban of AI generated content applies to all parts of the projects, including, but not limited
+to, code, documentation, issues, and artworks. An exception applies for purely translating texts
+for issues and comments to English.
+
+AI tools can be used to answer questions and find information. However, we encourage contributors
+to avoid them in favor of using [existing documentation](https://developer.gnome.org) and our
+[chats and forums](https://welcome.gnome.org). Since AI generated information is frequently
+misleading or false, we cannot supply support on anything referencing AI output.
 
 ## Pull Request Process
 
@@ -25,45 +43,6 @@ Please note we have a code of conduct, please follow it in all your interactions
 4. You may merge the pull request in once you have the sign-off of the maintainers, or if you
    do not have permission to do that, you may request the second reviewer to merge it for you.
 
-## Code of Conduct
-
-GNOME Calendar is a project developed based on GNOME Code of Conduct. You can read it below:
-
-### Summary
-
-GNOME creates software for a better world. We achieve this by behaving well towards
-each other.
-
-Therefore this document suggests what we consider ideal behaviour, so you know what
-to expect when getting involved in GNOME. This is who we are and what we want to be.
-There is no official enforcement of these principles, and this should not be interpreted
-like a legal document.
-
-### Advice
-
- * **Be respectful and considerate**: Disagreement is no excuse for poor behaviour or personal
-     attacks. Remember that a community where people feel uncomfortable is not a productive one.
-
- * **Be patient and generous**: If someone asks for help it is because they need it. Do politely
-     suggest specific documentation or more appropriate venues where appropriate, but avoid
-     aggressive or vague responses such as "RTFM".
-
- * **Assume people mean well**: Remember that decisions are often a difficult choice between
-     competing priorities. If you disagree, please do so politely. If something seems outrageous,
-     check that you did not misinterpret it. Ask for clarification, but do not assume the worst.
-
- * **Try to be concise**: Avoid repeating what has been said already. Making a conversation larger
-     makes it difficult to follow, and people often feel personally attacked if they receive multiple
-     messages telling them the same thing.
-
-
-In the interest of fostering an open and welcoming environment, we as
-contributors and maintainers pledge to making participation in our project and
-our community a harassment-free experience for everyone, regardless of age, body
-size, disability, ethnicity, gender identity and expression, level of experience,
-nationality, personal appearance, race, religion, or sexual identity and
-orientation.
-
 ## About GNOME Calendar  
 
 Learn more about GNOME Calendar by reading our [HACKING.md](HACKING.md) file.