add command shortcuts & menu command

public/_locales/en/messages.json

@@ -4,5 +4,8 @@
   },
   "app_description": {
     "message": "A minimalist bilingual translation Extension & Greasemonkey Script"
+  },
+  "toggle_translate": {
+    "message": "Toggle Translate"
   }
 }

public/_locales/zh_CN/messages.json

@@ -4,5 +4,8 @@
   },
   "app_description": {
     "message": "一个简约的双语网页翻译扩展 & 油猴脚本"
+  },
+  "toggle_translate": {
+    "message": "切换翻译"
   }
 }

public/manifest.firefox.json

@@ -15,6 +15,14 @@
       "matches": ["<all_urls>"]
     }
   ],
+  "commands": {
+    "toggleTranslate": {
+      "suggested_key": {
+        "default": "Alt+Q"
+      },
+      "description": "__MSG_toggle_translate__"
+    }
+  },
   "permissions": ["<all_urls>", "storage"],
   "icons": {
     "16": "images/logo16.png",

public/manifest.json

@@ -16,6 +16,14 @@
       "matches": ["<all_urls>"]
     }
   ],
+  "commands": {
+    "toggleTranslate": {
+      "suggested_key": {
+        "default": "Alt+Q"
+      },
+      "description": "__MSG_toggle_translate__"
+    }
+  },
   "permissions": ["storage"],
   "host_permissions": ["<all_urls>"],
   "icons": {