Add note that token methods don't backtrack and what that means.This should be helpful to newcomers.

Author: alexandrianlibrarian

doc/Language/grammar_tutorial.pod6

@@ -73,7 +73,9 @@ As already mentioned, grammars are declared using the I<grammar> keyword and its
 =item Regex methods are slow but thorough, they will look back in the string
 and really try.
 
-=item Token methods are faster than regex methods and ignore whitespace.
+=item Token methods are faster than regex methods and ignore
+whitespace. Token methods don't backtrack; they give up after the first
+possible match.
 
 =item Rule methods are the same as token methods except whitespace
 is not ignored.