sphinx-build --help missing -M option

Describe the bug

When using --help to fetch the documentation for the sphinx-build command, the -M option for the command does not show up as documented.

Using sphinx v5.0.2 on Ubuntu 22.04

I think this is somewhat relevant because the Makefile for generating the docs contains the -M option in its commands, so for a user exploring this could cause confusion.

How to Reproduce

$ sphinx-build --help

OS

Ubuntu 22.04

Python version

Python 3.10.4

Sphinx version

v5.0.2