Doc: Setting \qtvariable in module page.

\qtvariable indicates the QT variable needed in .pro files.

Change-Id: Iefd2cbc9f516cf3abb76b0f2fc2c009fb9a83900
Reviewed-by: Martin Smith <martin.smith@digia.com>

src/xmlpatterns/doc/src/qtxmlpatterns-module.qdoc

@@ -31,6 +31,7 @@
     XQuery, XSLT and XML Schema validation.
 
     \ingroup modules
+    \qtvariable xmlpatterns
 
 The \l{Qt XML Patterns} module provides support for XPath,
     XQuery, XSLT and XML Schema validation.