userguide/tasks: Added Basics section header.

docs/userguide/tasks.rst

@@ -7,6 +7,9 @@
 .. contents::
     :local:
 
+Basics
+======
+
 A task is a class that encapsulates a function and its execution options.
 Given a function ``create_user``, that takes two arguments: ``username`` and
 ``password``, you can create a task like this: