The `#versions_from_content` method requires a regex and this will be
enforced by the type signature, so we don't have to check for the
presence of a regex when handling a `strategy` block.
The initial documentation comments contained some remaining text
referring to `GithubLatest` and hadn't been updated to incorporate
the recent changes to the aforementioned strategy. This also reworks
some of the language to better explain the strategy's function,
application, etc.
