Add information about our PR merge policy

CONTRIBUTING.md

@@ -10,6 +10,18 @@ Just [file a GitHub issue](https://github.com/Automattic/simplenote-ios/issues/)
 
 If you’re filing a bug, specific steps to reproduce are helpful. Please include the part of the app that has the bug, along with what you expected to see and what happened instead.  A screenshot is always helpful as well.
 
-## Submitting code changes
+## Submitting Code Changes
 
-We welcome Pull Requests for bug fixes on any open issues that you'd like to contribute!
+We welcome Pull Requests for bug fixes on any open issues that you'd like to contribute!
+
+All code contributions pass through pull requests. If you haven't created a pull request before, we recommend this free video series, [How to Contribute to an Open Source Project on GitHub](https://egghead.io/courses/how-to-contribute-to-an-open-source-project-on-github).
+
+Note: If you are part of the org and have the permissions on the repo, don't forget to assign yourself to the PR, and add the appropriate GitHub label and Milestone for the PR
+
+### PR merge policy
+
+* PRs require one reviewer to approve the PR before it can be merged to the base branch
+* We keep the PR git history when merging (merge via "merge commit")
+* Who merges the PR once it's approved and green?
+  * For PRs authored by people external to the organisation and not having push permissions, the reviewer who approved the PR will merge it.
+  * For PRs authored by contributors with push permissions, the author of the PR will merge their own PR.