Footnote on GM20x fan control in PowerManagement.mdwn
I learnt in an IRC conversation with imirkin that fan speed control isn't possible from GM20x. I couldn't find this information anywhere else so I added it as a footnote to the table. IRC log: https://people.freedesktop.org/~cbrill/dri-log/index.php?channel=nouveau&highlight_names=&date=2021-09-14