Add missing 'Allow content merges' section title in project config documentation

Change-Id: I49dc89fabedf17996c5f8245b3fb024df2b2e6e3
diff --git a/Documentation/config-project-config.txt b/Documentation/config-project-config.txt
index 53e87ad..451e093 100644
--- a/Documentation/config-project-config.txt
+++ b/Documentation/config-project-config.txt
@@ -562,6 +562,7 @@
 the important distinction that Rebase Always does not ignore dependencies.
 
 [[content_merge]]
+=== Allow content merges
 If `Allow content merges` is enabled, Gerrit will try
 to do a content merge when a path conflict occurs.