Create book for docs - #13338

@iluuu1994 Awesome work! Thanks very much for coming up with this idea.

First, I was very surprised that the content of the internals book is not reused, but then I saw the (hidden) thread, so now the reason is clear. However, I'm wondering If there is anything left which still blocks the merge of this PR? As far as I see, the docs could be improved incrementally later on. For one, I'd like to contribute my part to the docs in the near future, that's why I'm asking this.

No blocker, I was waiting for feedback from the list. I also wanted to add some chapters first just to give an idea of the depth and language that is expected. I'll merge this PR soon.

@kocsismate Merged, any help with the documentation is appreciated 😊

It's been 2.5 years since this moved some files to docs-old. I ran a search over all repos in the org and these are nowhere linked. Internals discussions have a single mention of the directory itself, but no direct links to any files.

Do we think they are safe to delete now? Or alternatively, if we would want to keep their contents around, could we concatenate them into one (eg) docs/legacy.md (with a intro that makes clear that these are not current) to get rid of the docs-old directory?

cc @iluuu1994

They should be removed if they are outdated and/or bad. Otherwise they should be ported.