docs: Added note to Support Library Setup page: mediarouter to appcompat dependency

The v7 mediarouter support library depends on a couple of styles that are located
in the v7 appcompat library. This dependency requires developers to have both
libraries imported in their Eclipse workspace and to set up a library dependency
between the mediarouter to the appcompat library.

See Stackoverflow for issue and fix: http://goo.gl/xQI0Iw

Staging: http://joefernandez2.mtv.corp.google.com:8208/tools/support-library/setup.html#libs-with-res

Change-Id: Ifc7fa3dfcf9dfdb7faac7d2695a9988d49440c7d