Doc: Bare Metal Devices plugin

This topic needs more information about the
necessary Qt version and the "fake Qt" mentioned.
Also, I cannot try this in practice myself, so
steps might be missing.

Change-Id: I143a54b8559840c3e9ad6dd5d293de160d67867d
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
Reviewed-by: hjk <hjk121@nokiamail.com>