In particular, highlight more clearly cr50/common code differences,
describe update over USB state machine, and common code commands.
Also, replace all cr50/CR50 instances with Cr50.
BRANCH=none
BUG=b:36375666
TEST=~/chromium/src/tools/md_browser/md_browser.py -d docs
Change-Id: I45e26a87c3455e1c67be186b403b1d4c4acade91
Reviewed-on: https://chromium-review.googlesource.com/558537
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>