Add basic dev documentation

Change-Id: I6de025c38fa87d4b70bdd4d8eaf261ced97716f2

.github/PULL_REQUEST_TEMPLATE.md

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+# Important Notice
+
+Patch submission and review is done through
+[Gerrit Code Review](https://gerrit-review.googlesource.com).
+Unfortunately we cannot pull your code as a Pull Request.
+
+__NO REVIEWS OR DISCUSSIONS will happen on GitHub__, all the
+[code collaboration](../Documentation/developer-guide.md)
+will take place on Gerrit.

documentation/developer-guide.md

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+# Developer Guide
+
+[TOC]
+
+## Code Review
+
+This project uses Gerrit for code review:
+https://gerrit-review.googlesource.com/
+which uses the ["git push" workflow][1] with server
+https://gerrit.googlesource.com/gerrit-monitoring. You will need a
+[generated cookie][2].
+
+[1]: https://gerrit-review.googlesource.com/Documentation/user-upload.html#_git_push
+[2]: https://gerrit.googlesource.com/new-password
+
+Gerrit depends on "Change-Id" annotations in your commit message.
+If you try to push a commit without one, it will explain how to
+install the proper git-hook:
+
+```
+curl -Lo `git rev-parse --git-dir`/hooks/commit-msg \
+    https://gerrit-review.googlesource.com/tools/hooks/commit-msg
+chmod +x `git rev-parse --git-dir`/hooks/commit-msg
+```
+
+Before you create your local commit (which you'll push to Gerrit)
+you will need to set your email to match your Gerrit account:
+
+```
+git config --local --add user.email foo@bar.com
+```
+
+Normally you will create code reviews by pushing for master:
+
+```
+git push origin HEAD:refs/for/master
+```