Add example of channel mobility metrics to documentation

[elbeejay]

A working example of the channel mobility metrics (at least in their pre-merged form) is available here.

It would be good to incorporate this example or something similar to the DeltaMetrics documentation proper.

[amoodie]

Note this documentation exists:
https://deltarcm.org/DeltaMetrics/guides/subject_guides/mobility.html

This documentation could be expanded to include a parameter fit? Some brief narrative about the different metrics? Anything else you would want to add?