init from https://github.com/Hufe921/canvas-editor

docs/en/guide/plugin-custom.md

@@ -0,0 +1,25 @@
+# Custom Plugin
+
+::: tip
+Official plugin: https://github.com/Hufe921/canvas-editor-plugin
+:::
+
+## 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 = () => {}
+
+  // 3. listener, eventbus, shortcut, contextmenu, override...
+}
+```
+
+## Use Plugin
+
+```javascript
+instance.use(myPlugin, options?: Option)
+```