update postalcode only structured search doc

structured-geocoding.md

@@ -115,7 +115,7 @@ _Examples_
 * [CV23 9SL](https://whosonfirst.mapzen.com/spelunker/id/454261459/)
 * [5439171](https://whosonfirst.mapzen.com/spelunker/id/538904173/)
 
-Keep in mind that you cannot search for `postalcode` exclusively because postal codes are not imported as separate records. For example, this request [/v1/search/structured?postalcode=87801](http://search.mapzen.com//v1/search/structured?postalcode=87801) returns an error.
+Keep in mind that you can search for `postalcode` exclusively. So requests like [/v1/search/structured?postalcode=87801](http://search.mapzen.com//v1/search/structured?postalcode=87801) will return matching postalcode records.
 
 ### country