Add links to respectful changes/code reviews to code review documentation.

Change-Id: I07e088d2b98be4bb7872e69a730b618b9258d734
Reviewed-on: https://chromium-review.googlesource.com/728367Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Annie Sullivan <sullivan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510215}

docs/code_reviews.md

@@ -23,6 +23,9 @@ If you have multiple reviewers, make it clear in the message you send
 requesting review what you expect from each reviewer. Otherwise people might
 assume their input is not required or waste time with redundant reviews.
 
+Please also read [Respectful Changes](cl_respect.md) and
+[Respectful Code Reviews](cr_respect.md).
+
 #### Expectations for all reviewers
 
   * Aim to provide some kind of actionable response within 24 hours of receipt