README: Add contributing section

Author: jcfr

README.md

@@ -16,20 +16,69 @@ SlicerExecutionModel is documented here: https://www.slicer.org/wiki/Documentati
 Contributing
 ------------
 
-Once you've made your great commits:
+There are many ways to contribute to SlicerExecutionModel, with varying levels of effort. Do try to
+look through the documentation first if something is unclear, and let us know how we can
+do better.
 
-1. [Fork][fk] SlicerExecutionModel
-2. Create a topic branch - `git checkout -b my_branch`
-3. Push to your branch - `git push origin my_branch`
-4. Create an [Issue][is] with a link to your branch
-5. That's it!
+- Ask a question on the [Slicer forum][forum]
+- Submit a feature request or bug, or add to the discussion on the [issue tracker][is]
+- Submit a [Pull Request][pr] to improve the SlicerExecutionModel or its documentation
 
+We encourage a range of contributions, from patches that include passing tests and
+documentation, all the way down to half-baked ideas that launch discussions.
 
-Meta
-----
+### How to submit a PR
 
-* Code: `git clone git://github.com/Slicer/SlicerExecutionModel`
-* Bugs: <http://github.com/Slicer/SlicerExecutionModel/issues>
+If you are new to SlicerExecutionModel development and you don't have push access to the
+SlicerExecutionModel repository, here are the steps:
+
+1. [Fork and clone](https://help.github.com/articles/fork-a-repo/) the repository.
+2. Create a branch.
+3. [Push](https://help.github.com/articles/pushing-to-a-remote/) the branch to your GitHub fork.
+4. Create a [Pull Request][pr].
+
+This corresponds to the ``Fork & Pull Model`` mentioned in the
+[GitHub flow](https://guides.github.com/introduction/flow/index.html) guides.
+
+If you have push access to SlicerExecutionModel repository, you could simply push your branch
+into the main repository and create a [Pull Request][pr]. This
+corresponds to the ``Shared Repository Model`` and will facilitate other developers to checkout your
+topic without having to [configure a remote](https://help.github.com/articles/configuring-a-remote-for-a-fork/).
+It will also simplify the workflow when you are *co-developing* a branch.
+
+When submitting a PR, make sure to add a ``Cc: @slicer/slicerexecutionmodel`` comment to notify SlicerExecutionModel
+developers of your awesome contributions. Based on the
+comments posted by the reviewers, you may have to revisit your patches.
+
+### Automatic testing of pull requests
+
+When you submit a PR to the SlicerExecutionModel repo, CircleCI will run the build and test suite on the
+head of the branch. If you add new commits onto the branch, those will also automatically
+be run through the CI process. The status of the CI process (passing, failing, or in progress) will
+be displayed directly in the PR page in GitHub.
+
+The CircleCI build will run according to the [circle.yml file](circle.yml),
+which is useful as an example for how to set up your own environment for testing.
+
+Your test results will be posted on [SlicerExecutionModel's dashboard](http://slicer.cdash.org/index.php?project=SlicerExecutionModel).
+These results will list any failed tests. You can reach your
+build by clicking the build status link on your GitHub PR.
+
+### How to integrate a PR
+
+Getting your contributions integrated is relatively straightforward, here is the checklist:
+
+- All tests pass
+
+- Consensus is reached. This requires that a reviewer adds an "approved" review via GitHub with no
+  changes requested, and a reasonable amount of time passed without anyone objecting.
+
+Next, there are two scenarios:
+
+- You do NOT have push access: A SlicerExecutionModel core developer will integrate your PR.
+- You have push access: Simply click on the "Merge pull request" button.
+
+Then, click on the "Delete branch" button that appears afterward.
 
 License
 -------
@@ -45,4 +94,6 @@ limitations under the License.
 
 [fk]: http://help.github.com/forking/
 [is]: http://github.com/Slicer/SlicerExecutionModel/issues
+[pr]: http://github.com/Slicer/SlicerExecutionModel/pulls
+[forum]: https://discourse.slicer.org/