CDRIVER-734: documentation says "Returns blah"

Author: bjori

doc/mongoc_index_opt_get_default.page

@@ -18,11 +18,12 @@
     <synopsis><code mime="text/x-csrc"><![CDATA[const mongoc_index_opt_t *
 mongoc_index_opt_get_default (void) BSON_GNUC_CONST;
 ]]></code></synopsis>
+
   </section>
 
   <section id="return">
     <title>Returns</title>
-    <p>Returns blah</p>
+    <p>Returns a pointer to the default index creation options.</p>
   </section>