Add MTF-01 flow sensor setup instructions

[rmackay9]

This comes from this discussion in the Copter-4.5 forum where a user couldn't get it working. This is the 2nd report and the issue is that the sensor ships with a sysid=1, compid=1 which conflicts with the autopilot's default mavlink sysid/compid and in 4.5 we throw away these messages.

We should add a wiki page so that people can at least find the solution. The sensor also has a narrow field of view (6deg) and a build in 8m lidar so it's a decent choice I think.

[Hwurzburg]

Done #5922 awaiting your review