describe default GRASS_ADDON_PATH

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@46866 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/init/variables.html

@@ -112,7 +112,7 @@ text
   <dt>GRASS_ADDON_PATH</dt>
   <dd>[grass startup script]<br>
     allows to specify additional paths to local GRASS modules extra
-    to standard distribution.</dd>
+    to standard distribution. The default on GNU/Linux is $HOME/.grass7/addons</dd>
   
   <dt>GRASS_ADDON_ETC</dt>
   <dd>[libgis, g.findetc]<br>