README: Added Pygments requirement

Author: rdworth

README.md

@@ -7,8 +7,9 @@
 ### Requirements
 * <a href="http://www.xmlsoft.org/">libxml2</a>
 * <a href="http://xmlsoft.org/XSLT/">libxslt</a>
+* <a href="http://pygments.org/">Pygments</a>
 
-The `xmllint` and `xsltproc` utilities need to be in your path. If you are on Windows, you can get libxml2 and libxslt from <a href="http://sourceforge.net/projects/gnuwin32/files/">GnuWin32</a>.
+The `xmllint` and `xsltproc` and `pygmentize` utilities need to be in your path. If you are on Windows, you can get libxml2 and libxslt from <a href="http://sourceforge.net/projects/gnuwin32/files/">GnuWin32</a>.
 
 ### Build