[Best Practice] Add possible note about overriding 3rd party bundles

[weaverryan]

There are some very legitimate use-cases for multiple bundles, including (of course) when you're creating something that'll be shared between projects/kernels.

But I think another legitimate use-case is when you're overriding something in a re-usable bundle (e.g. controller). I think a note should be added to the BP about this.

See: https://twitter.com/EnekoOrma/status/543375361875410944

Thanks!

[wouterj]

I agree