g.parser manual: mention OR rules

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@64173 15284696-431f-4ddb-bdfa-cd5b030d7da7

general/g.parser/g.parser.html

@@ -112,6 +112,15 @@ The syntax of the rules section is following:
 #%end
 </pre></div>
 
+The parser also allows to define "OR" conditions, e.g. requiring raster OR vector:
+
+<div class="code"><pre>
+#%rules
+#% requires: raster, vector
+#%end
+</pre></div>
+
+
 <h2>NOTES</h2>
 
 An option can be instructed to allow multiple inputs by adding the