Update contributing.rst to include guidelines on Code Review

An important part of contributing to the Trove project is to review
changes proposed by others. To reflect the value of this activity, and
provide some guidelines on how the Trove project would like reviews to
be conducted, I have updated the contributing.rst file with a summary
of some conversations at the mid-cycle meetup.

The intent is that reviews of this proposed change will be a
discussion not only of the summary that I have attempted to capture,
but also of the change(s) being proposed.

I've opted to provide only rough guidelines and not provide exhaustive
examples of "good" and "bad" reviews (the format used by, for example,
the commit message guidelines) because the intent is not to create
rigid and cumbersome process but rather to provide guidelines that
reflect the desired purpose of the review process.

It is acceptable to -1 this change if you find typographical errors,
or have suggestions on the formatting of the document ;)

Change-Id: I09432c335282c17974cb62b6f77cd00ebcdda21f

CONTRIBUTING.rst

@@ -14,3 +14,64 @@ Pull requests submitted through GitHub will be ignored.
 Bugs should be filed on Launchpad, not GitHub:
 
    https://bugs.launchpad.net/trove
+
+Code Reviews
+------------
+
+We value your contribution in reviewing code changes submitted by
+others, as this helps increase the quality of the product as well.
+The Trove project encourages the guidelines (below).
+
+   - A rating of +1 on a code review is indicated if:
+
+     * It is your opinion that the change, as proposed, should be
+       considered for merging.
+
+
+   - A rating of 0 on a code review is indicated if:
+
+     * The reason why you believe that the proposed change needs
+       improvement is merely an opinion,
+     * You have a question, or need a clarification from the author,
+     * The proposed change is functional but you believe that there is
+       a different, better, or more appropriate way in which to
+       acheive the end result being sought by the proposed change,
+     * There is an issue of some kind with the Commit Message,
+       including violations of the Commit Message guidelines,
+     * There is a typographical or formatting error in the commit
+       message or the body of the change itself,
+     * There could be improvements in the test cases provided as part
+       of the proposed change.
+
+
+   - A rating of -1 on a code review is indicated if:
+
+     * The reason why you believe that the proposed change needs
+       improvement is irrefutable, or it is a widely shared opinion as
+       indicated by a number of +0 comments,
+     * The subject matter of the change (not the commit message)
+       violates some well understood OpenStack procedure(s),
+     * The change contains content that is demonstrably inappropriate,
+     * The test cases do not exercise the change(s) being proposed,
+     * You believe that the patch needs further work before it can be
+       merged.
+
+
+Some other reviewing guidelines:
+
+   - In general, when in doubt, a rating of 0 is advised,
+   - The code style guidelines accepted by the project are part of
+     tox.ini, a violation of some other hacking rule(s), or pep8 is
+     not a reason to -1 a change.
+
+Other references:
+
+   - https://wiki.openstack.org/wiki/CodeReviewGuidelines
+   - https://wiki.openstack.org/wiki/How_To_Contribute
+   - https://wiki.openstack.org/wiki/ReviewChecklist
+   - https://wiki.openstack.org/wiki/GitCommitMessages
+   - http://docs.openstack.org/developer/hacking/
+   - https://review.openstack.org/#/c/116176/
+
+
+