Put "getting started" in the part of the wiki that's for developers

[lkuper]

The https://github.com/mozilla/rust/wiki/Doc-getting-started page dates back to before we had releases, so the directions given there are how to build from git, not how to install a release. Now that we have releases, I think it makes sense to distinguish between installation instructions for developers and installation instructions for users. So that page should probably be in the "Notes" section of the wiki (for developers), and it probably needs a name like "getting started developing Rust".

[lkuper]

Done. The page is now https://github.com/mozilla/rust/wiki/Note-getting-started-developing-Rust.