docs: Fix typo - XH711 instead of HX711

[kabroxiko]

Fix documentation typo

[KevinOConnor]

Thanks. Commits need to have a signed-off-by line for me to commit directly (see https://github.com/Klipper3d/klipper/blob/master/docs/CONTRIBUTING.md ). If that is an issue, I'll make the corresponding fix using my sign off.

-Kevin

[KevinOConnor]

I fixed this in commit 5533999.

Thanks,
-Kevin