updated docs

docs/docs/linear_algebra.xml

@@ -1002,7 +1002,8 @@
          <spec_file link="true">dlib/geometry/point_transforms_abstract.h</spec_file>
          <description>        
             This is an object that applies an affine transformation to a <a href="#vector">vector</a> or 
-            <a href="#point">point</a>.
+            <a href="#point">point</a>.  Note that you can use <a href="#find_affine_transform">find_affine_transform</a>
+            to easily create affine transforms from sets of point correspondences.
          </description>
                                  
       </component>