meetup: improve descriptions by saying why each case is tested (#1919)
meetup: improve descriptions by saying why each case is tested (#1919)

descriptions show whether a date is the first, last, or an arbitrary
middle date of the week. This helps understand why certain cases are
selected.

Closes https://github.com/exercism/problem-specifications/issues/974
exercism/x-common,exercism/x-common,jmluy/x-common,jmluy/x-common,jmluy/x-common