Bug 1390938: only use one top-level heading; r=bstack

MozReview-Commit-ID: DKRdlCx6Ng8

--HG--
extra : rebase_source : 635ad93222038031fa3c41889d1572f56f289f05

taskcluster/docs/actions.rst

@@ -21,8 +21,8 @@ At a very high level, the process looks like this:
    for carrying out the named action, and may create new sub-tasks if necessary
    (for example, to re-trigger a task).
 
-Action Task Implementation
-==========================
+Defining Action Tasks
+---------------------
 
 There are two options for defining actions: creating a callback action, or
 creating a custom action task.  A callback action automatically defines an