[Docs] CLI command to serve docs locally (#6956)

* CLI command to serve docs locally

* Document it

* Default port

* Use `with` and subclass `SimpleHTTPRequestHandler` to set working dir

* Apply suggestions from code review

Co-Authored-By: skullydazed <skullydazed@users.noreply.github.com>

* Update docs/cli.md

lib/python/qmk/cli/__init__.py

@@ -5,6 +5,7 @@ We list each subcommand here explicitly because all the reliable ways of searchi
 from . import cformat
 from . import compile
 from . import config
+from . import docs
 from . import doctor
 from . import hello
 from . import json