Advertise 'graph' command of command line interface

src/coalg/coalg.ml

@@ -46,7 +46,7 @@ let _ =
 
 let printUsage name =
   print_endline ("Usage: \"" ^ name ^ " <task> <functor> [<flags>]\" where");
-  print_endline "       <task> in { sat print verify nnf prov (is »not.(sat ¬f)«) nom2fix }";
+  print_endline "       <task> in { sat print graph verify nnf prov (is »not.(sat ¬f)«) nom2fix }";
   print_endline "       <functor> in { MultiModalK (or equivalently K)";
   print_endline "                      MultiModalKD (or equivalently KD)";
   print_endline "                      Monotone";