Clarify how to pick a bridge type in the documentation

Tentatively targeting 6.0.0.CR1, but we could do this between 6.0.0.CR1 and 6.0.0.Final.

It looks like the current documentation is a bit overwhelming and doesn't help a lot when users wonder which type of bridge they should pick.

Maybe we should:

• Add examples of use to the "Basics" section: a very simple mapping where the bridge is applied, and a representation of the resulting index schema.

• Add the same example and representation of the resulting index schema to the section about each bridge type?