adding usecases page.

Author: mojitoj

xml/FHIR-security-label-ds-for-p.xml

@@ -35,6 +35,7 @@
     <page key="many" name="(many)"/>
     <page key="artifacts" name="Artifacts Summary"/>
     <page key="background" name="Background"/>
+    <page key="usecases" name="Use Cases"/>
     <page key="spec" name="Detailed Specification"/>
     <page key="changes" name="IG Change History"/>
     <page key="index" name="Security Label DS4P Home Page"/>