Add a subheading to make the start of the procedure clearer

Author: dacharyc

source/sdk/sync/partition-based-sync.txt

@@ -86,6 +86,9 @@ You might want update your client codebase when:
 - You add or change functionality that involves reading or writing SDK objects.
 - You want to implement more fine-grained control over what data you sync.
 
+Convert Partition-Based Sync Client Code to Use Flexible Sync
+`````````````````````````````````````````````````````````````
+
 Make these changes to convert your Partition-Based Sync client code to use 
 Flexible Sync: