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

Change by miss-islington <mariatta.wijaya+miss-islington@gmail.com>: ---------- nosy: +miss-islington nosy_count: 4.0 -> 5.0 pull_requests: +17999 pull_request: https://github.com/python/cpython/pull/18633 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue39654> _______________________________________