docs: support document internationalization #222

* docs: add English docuemnt #213

* docs: support document internationalization #222

---------

Co-authored-by: Hufe921 <huangyunfeihufe@hotmail.com>

docs/en/guide/plugin.md

@@ -0,0 +1,23 @@
+# Custom Plugin
+
+::: warning
+Currently, only methods can be added and modified to the editor instance, and more functions will be extended in the future
+:::
+
+## Write a Plugin
+
+```javascript
+export function myPlugin(editor: Editor, options?: Option) {
+  // 1. update，see more：src/plugins/copy
+  editor.command.updateFunction = () => {}
+
+  // 2. add，see more：src/plugins/markdown
+  editor.command.addFunction = () => {}
+}
+```
+
+## Use Plugin
+
+```javascript
+instance.add(myPlugin, options?: Option)
+```