Document -system-sqlite configuration parameter

-system-sqlite should be used when system SQLite library should be
used instead of the one embedded in Qt. This information is added
to SQLite driver documentation.

Change-Id: Ie51cb0d7c4044b74a64192ad8a5c946e21ee0ed9
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

doc/src/sql/sql-programming/sql-driver.qdoc

@@ -635,7 +635,9 @@
     \c{-qt-sql-sqlite} (linked directly into the Qt library).
 
     If you don't want to use the SQLite library included with Qt, you
-    can build it manually (replace \c $SQLITE by the directory where
+    can pass \c{-system-sqlite} to the configure script to use sqlite
+    libraries in the operating system. Alternatively, you can build
+    it manually (replace \c $SQLITE by the directory where
     SQLite resides):
 
     \snippet doc/src/snippets/code/doc_src_sql-driver.qdoc 21