zmake: Add reference to zmake unit test coverage
zmake: Add reference to zmake unit test coverage

Add a link to the latest coverage report on gitlab.

BRANCH=None
BUG=b:219062927
TEST=None

Signed-off-by: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@google.com>
Change-Id: Ia42e70c245e11c4daa3b3642bd9ce99e18cb99d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3489262
Reviewed-by: Al Semjonovs <c3a2ecb550cad1e7d5a943ca6241377f7b43ffc4@google.com>
Commit-Queue: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@chromium.org>
Tested-by: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@chromium.org>
Auto-Submit: Jeremy Bettis <4df7b5147fee087dca33c181f288ee7dbf56e022@chromium.org>

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