refer to existing files

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@35901 15284696-431f-4ddb-bdfa-cd5b030d7da7

swig/perl/index.dox

@@ -10,7 +10,11 @@ At the moment a prototype is implemented. It permits to use
 the GRASS raster command <em>r.slope.aspect</em> directly
 from the PERL programming language.
 <P>
-See: grass_wrap.c
+See: 
+
+  Grass.pm
+
+  R_slope_aspect/test.pl
 
 */