Update CONTRIBUTING.md to cover gitlab piplines

CONTRIBUTING.md

@@ -108,6 +108,9 @@ idea of the feature or fix to be developed given just the branch name.
         This is required as VTK-m uses Git-LFS to efficiently support data
         files.
 
+4.  If you are adding a new feature or making sigificant changes to API,
+    make sure to add a entry to `docs/changelog`. This allows release
+    notes to properly capture all relevant changes.
 
 ### Guidelines for Commit Messages ###
 
@@ -226,6 +229,10 @@ will be filled out for you.
 6.  The "**Assign to**", "**Milestone**", and "**Labels**" fields may be
     left blank.
 
+7.  Enable the "**Allow commits from members who can merge to the target branch.**" option,
+    so that reviewers can modify the merge request. This allows reviewers to change
+    minor style issues without overwhelming the author with change requests.
+
 7.  Use the "**Submit merge request**" button to create the merge request
     and visit its page.
 
@@ -318,14 +325,31 @@ succeeds.
 
 ### Testing ###
 
-VTK-m has a [buildbot](http://buildbot.net) instance watching for merge
-requests to test. Each time a merge request is updated the buildbot user
-(@buildbot) will automatically trigger a new build on all VTK-m buildbot
-workers. The buildbot user (@buildbot) will respond with a comment linking
-to the CDash results when it schedules builds.
+Each time a merge request is created or updated automated testing
+is automatically triggered, and shows up under the pipeline tab.
 
-The buildbot user (@buildbot) will also respond to any comment with the
-form:
+Developers can track the status of the pipeline for a merge
+request by using the Pipeline tab on a merge request or by
+clicking on stage icons as shown below:
+
+![alt text](docs/build_stage.png "Pipeline")
+
+When trying to diagnose why a build or tests stage has failed it
+generally is easier to look at the pruned information reported
+on [VTK-m's CDash Dashboard](https://open.cdash.org/index.php?project=VTKM).
+To make it easier to see only the results for a given merge request
+you can click the `cdash` link under the external stage ( rightmost pipeline stage icon )
+
+![alt text](docs/external_stage.png "CDash Link")
+
+In addition to the gitlab pipelines the buildbot user (@buildbot) will respond
+with a comment linking to the CDash results when it schedules builds.
+
+The builds for VTK-m that show up as part of the `external` stage of the
+gitlab pipeline are driven via buildbot, and have a different workflow.
+When you need to do things such as retry a build, you must issue commands
+via comments of the following form. The buildbot user (@buildbot) will
+respond signify that the command has been executed
 
     Do: test