Review instructions and ensure that platform-specific instructions are clearly identified

[hamishwillee]

I had a discussion with Tridge, Randy, Grant about what mode is recommended on the different platforms.

The answer was that on Copter you use "AUTO" for normal waypoint missions, and "GUIDED" for "special" or dynamic behaviour ("follow balloon" whatever). Copter has support for mission and other commands in GUIDED mode.

For Plane, many commands don't make sense (e.g. you can't specify an arbitrary velocity vector and get the plane to fly backward). In addition, the code hasn't been written to support arbitrary commands in GUIDED mode so you have limited control over what you can do in the mode other than send the vehicle to a point. As a result GUIDED is not currently of much use. Instead, on plane the main way of using DroneKit is to create and dynamically update missions as needed.

This is a bit of a problem because it means most of our examples and API are copter specific.

I propose the following:

1. Create topics "Working with Plane" and "Working with Copter" etc OR "Using DroneKit on different Vehicle Types" (covering all the vehicles).
2. Update examples to add a line explaining what vehicles they have been tested/work with
3. Add additional examples for Plane showing how to do dynamic variation of mission. This would also work on Copter.

@mrpollo - thoughts?