Add an accompanying example of a file for the importMap option example (#2791)

* Add @emotion/babel-plugin importMap example

* Update packages/babel-plugin/README.md

Co-authored-by: Mateusz Burzyński <[email protected]>

Author: joel-jo-querypie

packages/babel-plugin/README.md

@@ -301,6 +301,13 @@ This option assumes that you are using something to make `@emotion/react`'s `jsx
 
 This option allows you to tell @emotion/babel-plugin what imports it should look at to determine what it should transform so if you re-export Emotion's exports, you can still use the Babel transforms
 
+An example file:
+
+```js
+import { anotherExport } from 'my-package';
+import { someExport, thisIsTheJsxExport } from 'some-package';
+```
+
 An example config:
 
 ```json