Mention that filter=grep in py-nutshell

Resolves #1420

Author: bduggan

doc/Language/py-nutshell.pod6

@@ -457,8 +457,8 @@ becomes either of these:
     ( { $_[0] + $_[1] } for (3,9) X (2,10) );
     ( -> (\i, \j) { i + j } for (3,9) X (2,10) );
 
-Using C<map> (which is just like Python's C<map>) is
-an alternative.
+Using C<map> (which is just like Python's C<map>) and
+C<grep> (which is like Python's C<filter>) is an alternative.
 
 =head2 Classes and Objects