Add coverage check (warning/catch error) if the sample size is below a defined threshold

[davidclarance]

From Alan Lee: Need to define the parameters for the threshold.

[bluehill]

I'd do something like:
if('number of cards for 1 or more pentads'<4){warning("Please note that one or more of your selected pentads has fewer than 4 cards: reporting rates will likely not be useful for this summary") # or whatever: where prior to this there is a check on the number of cards for a pentad or set of pentads.