Docs: add PR template and AI contribution guidelines

[clonker]

No description provided.

[nikola-matic]

I like this in principle and wouldn't be against merging it as is - the only 'negative' point about it is that I think we should have some automation for this (a separate job, or at least an automatic comment on external PRs), otherwise this will just get lost amongst the rest of our contribution guidelines, which most people don't seem to read anyway :)

[r0qs]

I like this in principle and wouldn't be against merging it as is - the only 'negative' point about it is that I think we should have some automation for this (a separate job, or at least an automatic comment on external PRs), otherwise this will just get lost amongst the rest of our contribution guidelines, which most people don't seem to read anyway :)

Maybe we can also add a similar message to the external PR action: https://github.com/argotorg/solidity/blob/develop/.github/workflows/welcome-external-pr.yml. It already mentions the contributing section of the docs, but it might be worth repeating that information in the bot comment as well.

[cameel]

Suggested change

	disclosure in the pull request is mandatory. If we determine that a PR contains undisclosed
	AI-generated content, we may close it.
	disclosure in the pull request is mandatory.
	If we determine that a PR contains undisclosed AI-generated content, we may close it.

[cameel]

The new text partially overlaps with our current greeter. We should merge it into this template. Especially the self-review checklist would probably work better as a checkbox here.

[cameel]

Perhaps we should add a checkbox acknowledging that the contribution is licensed the same as the repo? That would be much lighter than the DCO someone suggested earlier.