Documentation about cache without enable module

[guiajlopes]

Documentation about how use the module without the module is enabled

[Berdir]

The classloader registration is interesting, wondering if that really works in all cases. The parts below then seem to duplicate existing documentation, I don't really see why we need to duplicate that? The example yml file is already mentioned directly above, the redis services.yml could be combined with the other code snippet. And the cache bin settings are already above too.

See also #12, that's where the classloader thing was also mentioned. Would be great if you could start a PR for documenting the container cache bin, also OK to do it as a single PR.