multiple updates

+ remove meshtastic temporarily
+ update imladris to use desktop system
+ move signal-desktop to desktop-packages
+ update README

hw/orion/default.nix

@@ -4,8 +4,4 @@
     ./hardware-configuration.nix
     ../../configs/desktop.nix
   ];
-
-  environment.systemPackages = with pkgs; [
-    signal-desktop
-  ];
 }