Fix intro flow example

doc/flow.rst

@@ -53,7 +53,7 @@ An Example
 
         start:
         -
-            if_before: 2015-03-06 23:59:00
+            if_after: 2015-03-06 23:59:00
             if_has_role: [student, ta, instructor]
             if_has_fewer_sessions_than: 2
             may_start_new_session: True
@@ -69,8 +69,8 @@ An Example
 
         access:
         -
-            if_before: 2015-03-06 23:59:00
-            permissions: [view, modify, see_correctness]
+            if_after: 2015-03-06 23:59:02
+            permissions: [view, submit_answer, end_session, see_correctness]
 
         -
             permissions: [view, see_correctness, see_answer_after_submission]
@@ -81,6 +81,9 @@ An Example
         grade_identifier: test_quiz
         grade_aggregation_strategy: max_grade
 
+        grading:
+        -   credit_percent: 100
+
     pages:
 
     -
@@ -228,7 +231,7 @@ Overall structure
 
 .. class:: FlowRules
 
-    Found in the ``rules`` attribute of a flow.
+    Found in the ``rules`` attribute of a :class:`Flow`.
 
     .. attribute:: start