Move stability attribute section to std dev guide?

[compiler-errors]

https://rustc-dev-guide.rust-lang.org/stability.html probably could live in https://std-dev-guide.rust-lang.org/, since it's not that relevant to the compiler. Just a thought.

[tshepang]

does it apply only to std though, or should it perhaps move to forge

[compiler-errors]

I think the only place we really use stability attributes are the standard library.

[JohnTitor]

Yeah, and it's related to development rather than team management/governance/policy etc. so I'd prefer to have it on std-dev-guide (unless t-libs prefers to have it on forge).