doc: add shortcut usage with GM_registerMenuCommand

Author: gera2ld

content/api/gm.md

@@ -373,7 +373,9 @@ Returns the command's `caption` since VM2.12.5 or `id` since VM2.15.9.
     * <Field name="autoClose?" type="boolean" defaultValue="true" />
       Whether to auto-close the popup after the user invoked the command.
 
-If you want to add a shortcut, please see [vm.shortcut](https://github.com/violentmonkey/vm-shortcut).
+<InfoBox>
+  If you want to add a shortcut, please refer to [keyboard shortcut](/guide/keyboard-shortcuts/#shortcut-for-menu-command).
+</InfoBox>
 
 Here's how you can change the command in-place, thus preserving its relative position in the list of multiple commands:
 ```js

content/guide/keyboard-shortcuts/index.mdx

@@ -32,7 +32,7 @@ Add `@violentmonkey/shortcut` to the [meta block](/api/metadata-block/) of our s
 And access all exports under `VM.shortcut`:
 
 ```js
-VM.shortcut.register('c-i', () => {/* c-i pressed */});
+const { register } = VM.shortcut;
 ```
 
 ### Option 2. Installation
@@ -51,29 +51,27 @@ And use it in our code:
 
 ```js
 import { register } from '@violentmonkey/shortcut';
-
-register('c-i', () => {/* c-i pressed */});
 ```
 
-## Usage
+## Quick Start
 
-Now we can easily register a keyboard shortcut:
+Easily register a keyboard shortcut:
 
 ```js
 VM.shortcut.register('c-i', () => {
   console.log('You just pressed Ctrl-I');
 });
 ```
 
-We can even register a key sequence:
+Register a key sequence:
 
 ```js
 VM.shortcut.register('c-a c-b', () => {
   console.log('You just pressed Ctrl-A Ctrl-B sequence');
 });
 ```
 
-We can disable and enable all key bindings at any time:
+Disable and enable all key bindings at any time:
 
 ```js
 // Disable all key bindings temporarily
@@ -83,4 +81,23 @@ VM.shortcut.disable();
 VM.shortcut.enable();
 ```
 
+## Shortcut for Menu Command
+
+Register a menu command with a shortcut:
+
+```js
+const shortcut = 'c-g c-g';
+const name = 'Good Game';
+const handler = () => alert('Good Game!');
+
+// Register menu command
+const menuName = `${name} (${VM.shortcut.reprShortcut(shortcut)})`;
+GM_registerMenuCommand(menuName, handler);
+
+// Register shortcut
+VM.shortcut.register(shortcut, handler);
+```
+
+See [@violentmonkey/shortcut][vm-shortcut] for more advanced usage.
+
 [vm-shortcut]: https://github.com/violentmonkey/vm-shortcut