More docs for brew create generated formula tests

To assist those new to stuff.

Library/Homebrew/cmd/create.rb

@@ -124,8 +124,12 @@ class FormulaCreator
       end
 
       def test
-        # this will fail we won't accept that, make it test the program works!
-        system "/usr/bin/false"
+        # This test will fail and we won't accept that! It's enough to just
+        # replace "false" with the main program this formula installs, but
+        # it'd be nice if you were more thorough. Test the test with
+        # `brew test #{name}`. Remove this comment before submitting
+        # your pull request!
+        system "false"
       end
     end
     EOS