[docs] [issue39654] pyclbr: remove old references to class browser & add explain readmodule

Terry J. Reedy <tjreedy@udel.edu> added the comment: Unlike the 3.9 code and doc change in #39411, this doc change applies since 3.7. It does not conflict with #39411. ---------- versions: +Python 3.7, Python 3.8 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue39654> _______________________________________