add nix-search-tv overlay

overlays/default.nix

@@ -10,6 +10,20 @@
       lib
       ;
   in {
+    ns = pkgs.writeShellApplication {
+      name = "ns";
+      runtimeInputs = with pkgs; [
+        fzf
+        nix-search-tv
+      ];
+      text = builtins.readFile "${pkgs.nix-search-tv.src}/nixpkgs.sh";
+
+      excludeShellChecks = [
+        # SC2016 (info): Expressions don't expand in single quotes, use double quotes for that.
+        "SC2016"
+      ];
+    };
+
     angry-oxide = import ../packages/angryoxide {
       inherit pkgs lib;
     };