Add more descriptive comments to include/fan.h
Add more descriptive comments to include/fan.h

Just adding some comments.

BUG=chrome-os-partner:23530
BRANCH=none
TEST=none

Change-Id: Ib3955e9d97ad8aa642e6fe298c17e34d2c66fb1c
Signed-off-by: Bill Richardson <129945214b1d548d8e49b6c29c43094f8c78057f@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/175139

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