Add a link to the second edition

[jmdyck]

... and a warning that this edition isn't really being maintained.

See #39038 (comment)

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @steveklabnik (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

[steveklabnik]

/cc @rust-lang/docs @rust-lang/core

We haven't decided when to do something like this. Is now the time?

[GuillaumeGomez]

We started the discussion but nothing much. Maybe we should wait after the next meeting to give it a go or not?

[frewsxcv]

As such, we're not really editing this edition.

This doesn't seem entirely accurate. Although it doesn't get as much love as it used to, Book 1.0 still receives edits now and then:

https://github.com/rust-lang/rust/commits/master/src/doc/book

In my opinion, until we start suggesting Book 2.0, I think it makes sense to keep Book 1.0 on life support. So I don't think we should discourage people from editing Book 1.0.

[steveklabnik]

@jmdyck thank you for this PR, but I think I'm going to close it. Not because it's bad, exactly, but because with the impending merge of rust-lang/rfcs#1828, we will be covering this as part of that work, and it would go in a totally different place.

[jmdyck]

Okay.