Document the automark_dependency configuration option.

Author: RKrahl

doc/src/configuration.rst

@@ -14,3 +14,12 @@ Configuration file options can be set in the `ini file`.
       This is a builtin configuration of pytest itself.  Since
       pytest-dependency requires pytest 2.8.0 or newer, it is
       recommended to set this option accordingly.
+
+   automark_dependency
+      This is a flag.  If set to `False`, the default, the outcome of
+      a test will only be registered if the test has been decorated
+      with the :func:`pytest.mark.dependency` marker.  As a results,
+      all tests, the dependencies and the dependent tests must be
+      decorated.  If set to `True`, the outcome of all tests will be
+      registered.  It has the same effect as if all tests are
+      implicitly decorated with :func:`pytest.mark.dependency`.