Add sd as s

- sd is a simple alternative to sed
- as I want to use ianthehenry's `sd`, I'll use `s` rather than `sd` as the
  command, moving it via an overlay
diff --git a/modules/ssh.nix b/modules/ssh.nix
index fcd9254..49e2dd1 100644
--- a/modules/ssh.nix
+++ b/modules/ssh.nix
@@ -29,7 +29,6 @@
 
     home.shellAliases = {
       ssh = "kitty +kitten ssh";
-      s = "kitty +kitten ssh";
     };
   };
 }
diff --git a/modules/utilities.nix b/modules/utilities.nix
index 87b8657..99e1253 100644
--- a/modules/utilities.nix
+++ b/modules/utilities.nix
@@ -3,6 +3,11 @@
   # them
   config.environment.systemPackages = with pkgs; [
     jq
+    (sd.overrideAttrs (oldAttrs: {
+      postInstall = ''
+        mv $out/bin/sd $out/bin/s
+      '';
+    }))
     lnav
   ];