docs: add section for the regulator board

Add a section explaining the connections for the voltage regulator
evaluation board, plus a few more pictures. Resize the existing
pictures for better "fit" in the documentation.

BUG=None
TEST=Follow the instructions and get the expected results

Change-Id: I9f7a327960014cc9237395224c253b4659d89e4a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/electric-eel/+/3781284
Tested-by: Paul Fagerburg <pfagerburg@chromium.org>
Reviewed-by: Alexandru Stan <amstan@chromium.org>
5 files changed