wxGUI readme updated (debugging)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@44892 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/README

@@ -132,10 +132,10 @@ clear the display and start from scratch.
 
 5 - DEBUGGING
 
-To enable GUI debug messages on given level set GRASS_DEBUG_WX
-environment variable, e.g.
+To enable GUI debug messages on given level set WX_DEBUG environment
+variable, e.g.
 
-$ export GRASS_WX_DEBUG=3
+$ g.gisenv set="WX_DEBUG=3"
 
 
 6 - VECTOR DIGITIZER