doc: Move environment documentation to rST

Move this from the README to rST format.

Drop i2cfast since it is obviously obsolete and breaks the formatting.
Other changes and improvements are in a following patch.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Marek BehĂșn <marek.behun@nic.cz>
2 files changed