[docs] [issue21063] Touch up one-line descriptions of modules for module index

Change by miss-islington <mariatta.wijaya+miss-islington@gmail.com>: ---------- pull_requests: +16863 pull_request: https://github.com/python/cpython/pull/17381 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue21063> _______________________________________