Update docs (#360) (#361)

raster/r.mapcalc/r.mapcalc.html

@@ -216,6 +216,9 @@ This syntax permits the development of neighborhood-type filters within a single
 map or across multiple maps.
 <p>
 
+The neighborhood modifier cannot be used on maps generated within same <em>r.mapcalc</em>
+command run (see "KNOWN ISSUES" section).
+<p>
 
 <h3>Raster map layer values from the category file</h3>