add documentation for media bundle listener configuration

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed tickets | #302

adding missing documentation on a new feature.

i wonder if we should mention those listeners anywhere else? its not that obvious to me, and i guess its not very important for the user to know them. (they are important but are activated by default and don't need interaction).

/cc @rmsint