docs: zephyr: Add testing information about motionsense
docs: zephyr: Add testing information about motionsense

Add some general guidelines for tests that can be run to make sure that
motionsense was initialized correctly.

BRANCH=none
BUG=b:208437221
TEST=none

Signed-off-by: Yuval Peress <50dc11c009bd4d7e9d9d15a383c1743ce5ee82ef@google.com>
Change-Id: I06c0bb77373e149bca8eaee8d08a0581bd04fcab
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3459248
Reviewed-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec