consolidated script documentation into a single md file

wrote documentation on terminal sound effects

added a sound effect for `invoke`

added the function `build-drv`, which is a wrapper for nix-build that
puts the output nix store path to the derivation into an environment
variable instead of symlinking it in the current working directory

overlay/scripts/commands/invoke.nix

@@ -1,9 +1,10 @@
-{ pkgs }:
+{ pkgs, self }:
 pkgs.writeShellApplication {
   name = "invoke";
   text = ''
     cmd="$1"
     shift
+    playshellsound ${self}/assets/sound/invoke.wav
     nix run nixpkgs#"$cmd" -- "$@"
   '';
 }