Added text about removing '?' from url field when upgrading [SF#790326].

Author: Johannes Gijsbers

doc/upgrading.txt

@@ -115,6 +115,9 @@ search page using the macros detailed in the customisation doc section
 
 __ customizing.html#searching-on-categories
 
+Also, the url field in the query class no longer starts with a '?'. You'll need
+to remove this question mark from the url field to support queries.
+
 
 0.6.0 Notes for metakit backend users
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