r.viewshed manual: improved example screenshot; clickable

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@69472 15284696-431f-4ddb-bdfa-cd5b030d7da7

raster/r.viewshed/r.viewshed.html

@@ -184,14 +184,19 @@ r.viewshed input=elev_lid792_1m output=elev_lid792_1m_viewshed \
 </pre></div>
 
 <div align="center" style="margin: 10px">
-<img src="r.viewshed.png" border=0><br>
-<i>Viewshed</i>
+<a href="r.viewshed.png">
+<img src="r.viewshed.png" width="900" alt="r.viewshed example" border=0><br>
+</a>
+<i>Viewshed shown on shaded terrain (observer position in the north-east quadrant with white dot; 5m above ground)</i>
 </div>
 <!--
 # image generated using
 d.mon wx0
-d.rast elev_lid792_1m
-d.rast elev_lid792_1m_viewshed
+r.relief input=elev_lid792_1m output=elev_lid792_1m_shade
+d.mon wx0
+d.shade shade=elev_lid792_1m_shade color=elev_lid792_1m_viewshed
+d.legend elev_lid792_1m_viewshed
+d.barscale
 # save image to files
 # crop the background using Gimp or ImageMagic
 mogrify -trim *.png