Instructions for playing with MAVLink

[hamishwillee]

People who are interested in learning the protocol want to play around with code, and might not have a real vehicle.
We need instructions to help them do this without too much thinking - part of example code.

• Talk to a vehicle - connect and send messages.
• Talk to a GCS - pretend to be a vehicle
• Talk to example code server
• Talk to test suite ?

Probably just instructions to set up simulator in first place.