docs: update README with future plans

public/_locales/en/messages.json

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+{
+  "app_name": {
+    "message": "KISS Translator"
+  },
+  "app_description": {
+    "message": "A simple bilingual translation extension & Greasemonkey script"
+  },
+  "toggle_translate": {
+    "message": "Toggle Translate"
+  },
+  "toggle_style": {
+    "message": "Toggle Style"
+  },
+  "open_options": {
+    "message": "Open Options"
+  },
+  "open_tranbox": {
+    "message": "Translate Popup/Selected"
+  }
+}

public/_locales/zh_CN/messages.json

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+{
+  "app_name": {
+    "message": "简约翻译"
+  },
+  "app_description": {
+    "message": "一个简约的双语对照翻译扩展 & 油猴脚本"
+  },
+  "toggle_translate": {
+    "message": "开启翻译"
+  },
+  "toggle_style": {
+    "message": "切换样式"
+  },
+  "open_options": {
+    "message": "打开设置"
+  },
+  "open_tranbox": {
+    "message": "翻译弹窗/选中文字"
+  }
+}