Document how to release and add changelog entries

Fixes #732

CONTRIBUTING.rst

@@ -51,11 +51,33 @@ If you are unsure what that means, here is a set-up workflow you may wish to fol
 
      git push -u origin topic_of_your_contribution
 
-
 (If any of the above seems overwhelming, you can look up the `Git documentation
 <http://git-scm.com/documentation>`_ on the web.)
 
 
+Releases and Changelog
+----------------------
+
+Heudiconv uses the `auto <https://intuit.github.io/auto/>`_ tool to generate the changelog and automatically release the project.
+
+`auto` is used in the heudiconv github actions, which monitors the labels on the pull request.
+Heudiconv automation can add entries to the changelog, cut releases, and
+push new images to `dockerhub <https://hub.docker.com/r/nipy/heudiconv>`_.
+
+The following pull request labels are respected:
+
+    * major: Increment the major version when merged
+    * minot: Increment the minot version when merged
+    * patch: Increment the patch version when merged
+    * skip-release: Preserve the current version when merged
+    * release: Create a release when this pr is merged
+    * internal: Changes only affect the internal API
+    * documentation: Changes only affect the documentation
+    * tests: Add or improve existing tests
+    * dependencies: Update one or more dependencies version
+    * performance: Improve performance of an existing feature
+
+
 Development environment
 -----------------------