Update the readme file to have pyos information about the theme and what repos use the theme

[lwasser]

Right now the readme file has 2i2c. i did use Chris' theme as the base for this to learn!

https://github.com/2i2c-org/sphinx-2i2c-theme

so we want to acknowledge that in the readme as well.

see #2 for a list of repos that we use this theme in now.

[lwasser]

closing this one as not specific enough as well.