[4313] Added a comment about token order

src/lib/eval/parser.yy

@@ -34,6 +34,7 @@ using namespace isc::eval;
 }
 
 %define api.token.prefix {TOKEN_}
+// Tokens in an order which makes sense and related to the intented use.
 %token
   END  0  "end of file"
   LPAREN  "("