Update clang-tidy docs to suggest a release build of clang

TBR=dcheng@chromium.org

Change-Id: I19f39e02003e9d51a3c9eed0c17fc9208b958ab1
Reviewed-on: https://chromium-review.googlesource.com/786692
Commit-Queue: Chris Watkins <watk@chromium.org>
Reviewed-by: Chris Watkins <watk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#519036}
1 file changed