[clang] Move documentation about -verify from a header to public docs (PR #73694)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

Urgh, I finally set a bookmark on that page, so this is going to break that!

But yeah, this makes a lot more sense here, and I think ends up being easier to maintain.  It passes a quick proofread, so lgtm.

https://github.com/llvm/llvm-project/pull/73694