documented the new setenv command

doc/partiview.sgml

@@ -607,6 +607,7 @@ Determines the list of directories where all data files, color maps, etc.
 are sought.  See the <tt/filepath/ entry under
 <!-- ref id="datacommands" name="Data Commands" --> Data Commands.
 
+
 </descrip>
 
 <sect1>Object group commands
@@ -1394,6 +1395,13 @@ kira <it/file/
 read a <tt/kira/ formatted file. See the <tt/kiractl/ Control
 Command to modify the looks of the objects.
 
+<tag>
+setenv name value
+</tag>
+Add (or change) a named variable of the environment variables space of
+partiview. Enviroment variables, like in the normal unix shell, can be
+referred to by prepending their name with a $.
+
 <tag>
 object <it/gN=ALIAS/
 </tag>