mention v.rectify

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@52420 15284696-431f-4ddb-bdfa-cd5b030d7da7

doc/projectionintro.html

@@ -48,6 +48,10 @@ into the location with projection and geocoded within this location by
 defining  four corner points or by seeking several ground control points.
 These points are stored into an ASCII file and then transformed within 
 the same location (<a href="v.transform.html">v.transform</a>).
+
+Alternatively, <a href="v.rectify.html">v.rectify</a> rectifies a vector
+by computing a coordinate transformation for each object in the vector
+based on the control points. 
 <p>
 A graphical user interface is provided by <a href="gis.m.html">gis.m</a>.