[docs] [issue41411] Improve and consolidate f-strings docs

Change by Ama Aje My Fren <amaajemyfren@gmail.com>: ---------- pull_requests: +20825 pull_request: https://github.com/python/cpython/pull/21681 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue41411> _______________________________________