REQUIREMENTS.html: say what Python PLY is

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@62119 15284696-431f-4ddb-bdfa-cd5b030d7da7

REQUIREMENTS.html

@@ -149,7 +149,7 @@ Ctypes can be added as a third-party module in Python 2.3 and 2.4
 <a href="http://labix.org/python-dateutil">http://labix.org/python-dateutil</a>
 </li>
 
-<li><b>Python PLY Library</b> ("python-ply", needed for the temporal algebra in tgis)<br>
+<li><b>Python PLY Library (Python Lex-Yacc)</b> ("python-ply", needed for the temporal algebra in tgis)<br>
 <a href="http://www.dabeaz.com/ply">http://www.dabeaz.com/ply</a>
 </li>