autoFocus for richtexteditor

src/RichTextEditor.js

         Keyboard.addListener('keyboardDidShow', this._onKeyboardWillShow),
         Keyboard.addListener('keyboardDidHide', this._onKeyboardWillHide)
       ];
+      if (this.props.autoFocus) {
+        this.webview.requestFocus();
+      }
     }
   }