Update Overview.md (#2434)

Summary:
**Summary**

Import `Draft.css` in the getting started example.
Pull Request resolved: #2434

Reviewed By: claudiopro

Differential Revision: D21652152

Pulled By: mrkev

fbshipit-source-id: 27edcd7ec883fbb83c9dc06661ade9513f9f0b5d

Author: abdellani

docs/Overview.md

@@ -46,6 +46,7 @@ If you are interested in helping out, or tracking the progress, please follow
 import React from 'react';
 import ReactDOM from 'react-dom';
 import {Editor, EditorState} from 'draft-js';
+import 'draft-js/dist/Draft.css';
 
 class MyEditor extends React.Component {
   constructor(props) {
@@ -70,6 +71,7 @@ Since the release of React 16.8, you can use [Hooks](https://reactjs.org/docs/ho
 import React from 'react';
 import ReactDOM from 'react-dom';
 import {Editor, EditorState} from 'draft-js';
+import 'draft-js/dist/Draft.css';
 
 function MyEditor() {
   const [editorState, setEditorState] = React.useState(