Clarify where this K3 barcode font is coming from.

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@219012 13f79535-47bb-0310-9956-ffa450edef68

examples/fo/advanced/K3.README

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+The K3 3 of 9 barcode font is available from:
+
+http://www.geocities.com/keith_dimmock/
+
+Keith Dimmock states:
+Unless otherwise indicated all downloads are FREE, no cost and no nag screens.