meta: add AI disclosure markings/contribution guidelines (#273)

Author: avivace

CONTRIBUTING.md

@@ -47,6 +47,24 @@ If you are not confident in forking the repository, making the change and sendin
 
 Before the PR gets approved and merged, we may require a number of reviews from our contributors.
 
+### AI disclosure
+
+There are two different things to disclose: AI used to prepare your contribution, and AI used to make the resource you're adding.
+
+**Your contribution.** If AI tools helped you prepare your PR (e.g. finding the resource or writing its description), follow the [gbdev AI policy](https://gbdev.io/aipolicy.html) and add an `Assisted-by` tag to your commit message.
+
+**The resource.** Resources made with the help of AI are accepted, but they must be marked so readers can make up their own mind about them ([#273](https://github.com/gbdev/awesome-gbdev/issues/273)). Put the mark right after the link, before the description:
+
+- `†` - AI-assisted: the resource contains some AI-generated content (code, documentation, assets), even a small part such as a helper script or a few fixes.
+- `‡` - AI-generated: most of the resource was made by AI (e.g. "vibe-coded" projects).
+
+```
+- [resource](link) † - Description.
+- [resource](link) ‡ - Description.
+```
+
+Also mention the AI usage in your PR description, along with how you know about it (e.g. the author says so, the repository has an `AGENTS.md` or `CLAUDE.md`, an AI agent appears among the commit authors). If you're unsure which mark applies, say so in the PR and the maintainers will decide.
+
 ### Checking your changes locally
 
 CI runs two checks, here's how you can try them locally.

README.md

@@ -84,12 +84,17 @@ You can find a (way cooler) web version of this list [here](https://gbdev.github
 >If you aim to develop your software for SGB or GBC, or you want to know how it runs on the other systems, you may want to take advantage and adapt to these differences, check the [Game Boy Color](#game-boy-color) category and look for specific references to GBC/CGB and SGB.
 
 
+
+
 ## Community
 
 - [Chat channels](https://gbdev.io/chat)
 - [Forum](https://gbdev.gg8.se/forums/)
 
 <!-- gbdev.io:begin body -->
+
+> Resources marked with † are developed with AI/LLM usage, resources marked with ‡ were mostly generated by AI. See [AI disclosure](CONTRIBUTING.md#ai-disclosure).
+
 ## Documentation
 
 - [**Pan Docs**](https://gbdev.github.io/pandocs/) - The single, most comprehensive technical reference to Game Boy available to the public. Corrected, updated and maintained by the community.