Recommend buildbox-casd as remote cache

The current documentation recommends using buildbarn as remote cache. It is however overkill for small setups (single disk less than 1TB).

Instead, I would recommend buildbox-casd behind a reverse proxy (that provides TLS) for simple setups.

Start by locating the documentation that currently recommends buildbarn as a remote cache. Review the guidance for small setups and update it to recommend buildbox-casd behind a TLS-providing reverse proxy, with the documentation clearly covering the stated use case.

Written by the indexing model from the issue text.