Link to the main docs per https://github.com/mozilla/rust/pull/11123

According to this PR https://github.com/mozilla/rust/pull/11123

We're moving away from the wikis and we need to redirect users to this new transcribed internal documentation page.

# NOTE
This new documentation page will link to 0.9, which is not yet released. In case of this PR being ok, we need to deploy right after rust cuts the release to 0.9