Add note about un-mapping the bundle

[weaverryan]

Hey Stof-

I think we should add a note about un-mapping the bundle's entities, unless you want the Log or Translation entities. Basically, show auto_mapping can be true, but how the bundle's mapping can be turned off in the default entity manager. I use your bundle all the time - but usually just for Sluggable and Timestampable, so I do this commonly.

Thanks!