git: Use the GPG key on my Yubikey for signing commits

modules/programs/git/default.nix

@@ -12,6 +12,9 @@ in {
       enable = true;
       userEmail = "papatutuwawa@polynom.me";
       userName = "Alexander \"PapaTutuWawa\"";
+
+      # The key on my Yubikey
+      signing.key = "B688F70D0EC87D5A8A9D3D7A56C749835F3CE824";
       extraConfig = {
         init = {
           defaultBranch = "master";