Document cvc5-style numerals

This documents the addition of cvc5-style numerals.

spec/changelog.tex

@@ -33,7 +33,7 @@ Breaking changes:
         only determined by its syntactic category.
   \item The arguments for \proofRule{forall_inst} have been changed to
         no longer take the shape of bindings using \texttt{(:= x c)}.
-        Instead, the list of instatiation terms must follow the variable order.
+        Instead, the list of instatiation terms must follow the variable order and cover all the respective bound variables.
 \end{itemize}
 
 \noindent