feature(software): add signal-desktop electron app

INSTALLATION.md

@@ -159,6 +159,13 @@ $ sudo nix shell nixpkgs#tpm2-tools -c tpm2_eventlog /sys/kernel/security/tpm0/b
   (disable Secure Boot, `sbctl enroll-keys --tpm-eventlog`)
 - Without an integrated gpu (argon), the gpu's option ROM draws the firmware
   setup too, use `--microsoft` there, a refused gpu means no picture at all
+- On the Framework (krypton), keep the firmware's built-in OEM certificates
+  with `--firmware-builtin`, vendor firmware updates may need them. If an
+  update fails or the keys were enrolled without them, erase the keys in the
+  firmware again (Setup Mode) and re-enroll:
+```bash
+$ sudo sbctl enroll-keys --firmware-builtin
+```
 
 6. enable Secure Boot in the firmware and set a firmware password, then check
 ```bash

modules/home-manager/programs.nix

@@ -7,6 +7,7 @@
     discord
     fastfetch
     keepassxc
+    signal-desktop
     teamspeak6-client
     typst
     zathura