Make it clear that textarea also supports defaultValue. (#9318)

docs/uncontrolled-components.md

@@ -63,4 +63,4 @@ render() {
 }
 ```
 
-Likewise, `<input type="checkbox">` and `<input type="radio">` support `defaultChecked`, and `<select>` supports `defaultValue`.
+Likewise, `<input type="checkbox">` and `<input type="radio">` support `defaultChecked`, and `<select>` and `<textarea>` supports `defaultValue`.