r.neighbors manual: sync to trunk (https://trac.osgeo.org/grass/changeset/64860)

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@64897 15284696-431f-4ddb-bdfa-cd5b030d7da7

raster/r.neighbors/r.neighbors.html

@@ -9,7 +9,7 @@ function of the values in that cell's neighborhood.  For
 example, each cell in the output layer might be assigned a
 value equal to the average of the values
 appearing in its 3 x 3 cell "neighborhood" in the input
-layer.
+layer. Note that the centre cell is also included in the calculation.
 
 <h3>OPTIONS</h3>
 
@@ -159,8 +159,9 @@ The result is rounded to the nearest integer (in this case 64).
 <em>Neighborhood Size:</em>
 The neighborhood <b>size</b> specifies which cells surrounding any given
 cell fall into the neighborhood for that cell.
-The <b>size</b> must be an odd integer.
-For example,
+The <b>size</b> must be an odd integer and represent the lenght of one of
+moving window edges in cells.
+For example, a size value of 3 will result in
 <div class="code"><pre>
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