[3.11] GH-71383: IDLE - Document testing subsets of modules (GH-104463) (#104464)

GH-71383: IDLE - Document testing subsets of modules (GH-104463)
(cherry picked from commit 080a5961527473af182b025bb29e0c52d43fd49e)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>
3 files changed