Draft: docs: Add "Alyssa's driver survival guide"

Everything I want to say to a new dev on-boarding to an Alyssa driver.

IDK if mesa docs are the right place for this. Maybe will stick it on rosenzweig.io instead, or a wiki somewhere or something... Some of this is general Mesa how-to but a lot of it is specific to my drivers. Posting MR so I don't forget I wrote this.

If mesa docs is the right place it needs to be properly formatted as RST... that sounds like a good first commit to Mesa :-p

Signed-off-by: Alyssa Rosenzweig alyssa@collabora.com