gh-124370: Add "howto" for free-threaded Python #126358

Job	Run time
Change detection / Compute changed files	14s
Windows MSI${{ '' }}	0s
Windows ${{ ((fromJSON(matrix.free-threading) && '(free-threading)') \|\| '') }}	0s
Check if generated files are up to date	0s
macOS ${{ ((fromJSON(matrix.free-threading) && '(free-threading)') \|\| '') }}	0s
Ubuntu ${{ ((fromJSON(matrix.free-threading) && '(free-threading)') \|\| '') }}	0s
Ubuntu SSL tests with OpenSSL	0s
WASI	0s
Address sanitizer	0s
Thread sanitizer	0s
Thread sanitizer (free-threading)	0s
Hypothesis tests on Ubuntu	0s
CIFuzz	0s
Docs / Docs	1m 57s
Docs / Doctest	22m 34s
Docs / Docs (Oldest Sphinx)	2m 3s
All required checks pass	1s
	26m 49s

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