Emphasize that the app being in the background or locked screen results in connection loss

[MrCsabaToth]

The OS sooner or later will evict the app. At which point the recording also gets interrupted. David unknowingly ran into this.

We have a ticket about background support but it needs significant refactoring so there's no ETA.

Split screen is a workaround, "Fix empty workouts" in the Data Preferences can repair interrupted workouts to some extent.

[MrCsabaToth]

Ref TrackMyIndoorWorkout/TrackMyIndoorWorkout#527