Update telemetry.md; telemetry.subscribe_all_ok() does not exist

[raceking37]

Found a small error in the documentation: telemetry.subscribe_all_ok() doesn't exist, this was probably meant to be the telemetry.subscribe_health_all_ok() method.

[julianoes]

Thanks, makes sense.

There is the flag health.is_armable() which tells you whether arming is possible: https://github.com/mavlink/MAVSDK/blob/849cb9a3c3bd18d21731da3b0c4fe31ca6b9d039/src/mavsdk/plugins/telemetry/include/plugins/telemetry/telemetry.h#L410

[hamishwillee]

So what does healthy "mean" then in MAVlink terms? Yes I could look it up. I guess I'm hinting we need to be a bit more clear about how the data can be used in the docs.

[julianoes]

Healthy here is just my interpretation of good to fly, it doesn't mean anything. It's just a poor simplification of information that is now properly exposed in MAVLink but wasn't when it was designed 2016.

[hamishwillee]

Perhaps replace it with something more meaningful in next revision then?

[julianoes]

Perhaps yes.