r.mapcalc manual: refer to r.mapcalc.simple

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@73802 15284696-431f-4ddb-bdfa-cd5b030d7da7

raster/r.mapcalc/r.mapcalc.html

@@ -805,7 +805,8 @@ NULL cells. It is left to the user to utilize the <tt>isnull()</tt> function.
 <a href="r.bitpattern.html">r.bitpattern</a>,
 <a href="r.blend.html">r.blend</a>,
 <a href="r.colors.html">r.colors</a>,
-<a href="r.fillnulls.html">r.fillnulls</a>
+<a href="r.fillnulls.html">r.fillnulls</a>,
+<a href="r.mapcalc.simple.html">r.mapcalc.simple</a>
 </em>