Document the change in wxMSW wxToolBar height determination

Since 0185d61a2c wxToolBar height is
increased if the controls don't fit in it rather than decreasing the
size of the controls, which results in different appearance than in the
previous versions, so document this as well as the advice for restoring
the old behaviour.

docs/changes.txt

@@ -65,6 +65,11 @@ Changes in behaviour not resulting in compilation errors
 - wxGTK wxNotebook::AddPage() doesn't generate any events any more for the
   first page being added, for consistency with the other ports.
 
+- wxMSW wxToolBar height now adapts to the height of embedded controls, making
+  the toolbar taller if necessary, rather than making the controls smaller. To
+  return to the previous behaviour, you need to explicitly create controls of
+  smaller size.
+
 
 Changes in behaviour which may result in build errors
 -----------------------------------------------------