devshell: Add docs Markdown previewer

Wraps `go-grip` to preview docs in the browser before pushing,
rendered locally with live reload. Defaults to `docs/README.md`.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

devshell/commands.nix

@@ -59,6 +59,17 @@ in
       help = "SSH to a machine by NixOS system or home-manager config name";
       command = ''exec ${sshMachine}/bin/ssh-machine "$@"'';
     }
+    {
+      name = "docs";
+      category = "utilities";
+      help = "Preview Markdown docs in the browser (default: `docs/README.md`)";
+      command = ''
+        if [ $# -eq 0 ] || [[ "$1" == -* ]]; then
+          set -- "$PRJ_ROOT/docs/README.md" "$@"
+        fi
+        exec ${pkgs.go-grip}/bin/go-grip "$@"
+      '';
+    }
     {
       name = "json2nix";
       category = "utilities";

devshell/default.nix

@@ -33,5 +33,6 @@ in
     '')
     home-manager
     jujutsu
+    go-grip
   ];
 }

docs/deployment.md

@@ -116,6 +116,7 @@ command with no arguments for its help. From
 | `qemu-genmac` | Prints a random QEMU-suitable MAC (`52:54:00:xx:xx:xx`). |
 | `ssh-get-ed25519 <host>` | Prints a host's ed25519 pubkey via `ssh-keyscan`. |
 | `json2nix` | Converts JSON on stdin to formatted Nix. |
+| `docs [file] [go-grip args]` | Previews Markdown in the browser with `go-grip` (default `docs/README.md`), rendered locally with live reload. |
 
 From [`devshell/install.nix`](../devshell/install.nix) (driven by `$INSTALLER`, the address of
 a running custom installer, SSHing as root with `.keys/deploy.key`):