Adds missing `s` to sligthly odd sentence.

doc/tut2.txt

@@ -948,7 +948,7 @@ Generating AST by hand
 
 To generate an AST we would need to intimately know the structures used by the
 Nimrod compiler exposed in the `macros module <macros.html>`_, which at first
-look seems a daunting task. But we can use a helper shortcut the ``dumpTree``
+look seems a daunting task. But we can use as helper shortcut the ``dumpTree``
 macro, which is used as a statement macro instead of an expression macro.
 Since we know that we want to generate a bunch of ``const`` symbols we can
 create the following source file and compile it to see what the compiler