Update AI documentation

[InAnYan]

I think the new documentation is not deployed right now?

I also found a SUMMARY.md file, where there was no AI. So I made a separate PR for this

[koppor]

This is a follow-up to #491.

I do understand why here are so many changes. Need to look into it later.

[koppor]

I found the issue:

1. Add AI documentation #491 was squash-merged
2. This PR was based on the branch of Add AI documentation #491
3. A new commit ebcc0e1 (#497) was added

"Just" merging main fixes the issue of GitHub showing too much difference. - Always starting from main is also a workaround of the issue.

[koppor]

We do a bad job with our CONTRIBUTING guidelines.

Maybe you can help to move content from https://github.com/JabRef/user-documentation?tab=readme-ov-file#advanced-contribution-hints to https://github.com/JabRef/user-documentation/blob/main/en/contributing/how-to-improve-the-help-page.md. -- I think, it is "just" text moval?

[InAnYan]

Oliver, remember you told, that "Students don't think"

Student's (me) don't think :)

[InAnYan]

Ah, a squash-merge, I see. Sorry