add lua&sed to shell and switch to coq 8.11 + fixing doc

config.nix

@@ -1,3 +1,3 @@
 {
-  coq = "8.10";
+  coq = "8.11";
 }

default.nix

@@ -111,5 +111,7 @@ let
 in
 if pkgs.lib.trivial.inNixShell then pkg.overrideAttrs (old: {
   inherit shellHook mathcompnix;
-  buildInputs = (old.buildInputs or []) ++ pkgs.lib.optional withEmacs emacs;
+  buildInputs = (old.buildInputs or []) ++
+                pkgs.lib.optional withEmacs emacs ++
+                [ pkgs.lua pkgs.sedutil ];
 }) else pkg

mathcomp/ssreflect/order.v

@@ -117,7 +117,7 @@ From mathcomp Require Import path fintype tuple bigop finset div prime.
 (* 3. declaring notations for the main operations of this library, by         *)
 (*    setting the first argument of the definition to the display, e.g.       *)
 (*    `Notation my_syndef_le x y := @Order.le my_display _ x y.` or           *)
-(*    `Notation "x <<< y" := @Order.lt my_display _ x y (at level ...).`      *)
+(*    `Notation "x <=< y" := @Order.lt my_display _ x y (at level ...).`      *)
 (*    Non overloaded notations will default to the default display.           *)
 (*                                                                            *)
 (* One may use displays either for convenience or to disambiguate between     *)