Fix header of "Pitfalls" subsection of Private Changes documentation

Change-Id: I3dacba7ffd910122cf1dbd123276c6ef29fe5f14
(cherry picked from commit 2ba3b5a55d37315189104d4237c007bae01f908d)
diff --git a/Documentation/intro-user.txt b/Documentation/intro-user.txt
index 03f3880..6e58608 100644
--- a/Documentation/intro-user.txt
+++ b/Documentation/intro-user.txt
@@ -605,8 +605,7 @@
 exposing secret details.
 
 [[private-changes-pitfalls]]
-Pitfalls
-===
+=== Pitfalls
 
 If private changes are used, be aware of the following pitfalls: