Merge branch 'am/doc-sha256'

Tone down the warning on SHA-256 repositories being an experimental curiosity. We do not have support for them to interoperate with traditional SHA-1 repositories, but at this point, we do not plan to make breaking changes to SHA-256 repositories and there is no longer need for such a strongly phrased warning. * am/doc-sha256: doc: sha256 is no longer experimental