enable nested structure in topic navigation

Author: koperagen

docs/StardustDocs/project.ihp

@@ -7,4 +7,7 @@
     <images dir="images" version="0.9" web-path="images/" />
     <vars src="v.list"/>
     <product src="d.tree" version="0.9" id="dataframe"/>
+    <settings>
+        <default-property element-name="toc-element" property-name="show-structure-depth" value="2"/>
+    </settings>
 </ihp>