Update documentation for rational-valued functor

It was still refering to the old syntax.

src/Copar/Functors/GroupValued.hs

@@ -106,8 +106,8 @@ rationalHelp =
   <> Doc.annotate Doc.bold "Coalgebra syntax:"
   <+> Doc.reflow "'{' X ':' rational, ... '}'"
   <> Doc.line
-  <> Doc.reflow "  Note that rationals currently have the same syntax as reals \
-                \and proper fractions are not supported."
+  <> Doc.reflow "where 'rational' is either an integer or of the form a/b, \
+                \where a and b are integers."
 
 newtype OrderedComplex = OrderedComplex (Complex EqDouble)
   deriving (Eq, Num, NFData, Show)