distance_to_anomaly: specify unit of max distance in docstring / documentation in general

[Storch22]

Expected behaviour
Provide the unit of max distance in the docstring and general documentation. In the code, option is set to "DISTUNITS=GEO" and indicates that distances generated are in georeferenced coordinates (not pixel).

Current behaviour
Right now it is not clear to the user what unit the max distance has - pixel, meter, km,....