Update material-ui doc (#2715)

- Fix images
- Specify that it's version 4 and 5

packages/material-ui/README.md

@@ -14,7 +14,7 @@
   <h3 align="center">@rjsf/material-ui</h3>
 
   <p align="center">
-  Material UI theme, fields and widgets for <a href="https://github.com/rjsf-team/react-jsonschema-form/"><code>react-jsonschema-form</code></a>.
+  Material UI 4 and 5 themes, fields and widgets for <a href="https://github.com/rjsf-team/react-jsonschema-form/"><code>react-jsonschema-form</code></a>.
     <br />
     <a href="https://react-jsonschema-form.readthedocs.io/en/latest/"><strong>Explore the docs »</strong></a>
     <br />
@@ -166,6 +166,4 @@ GitHub repository: [https://github.com/rjsf-team/react-jsonschema-form](https://
 [npm-url]: https://www.npmjs.com/package/@rjsf/material-ui
 [npm-dl-shield]: https://img.shields.io/npm/dm/@rjsf/material-ui.svg?style=flat-square
 [npm-dl-url]: https://www.npmjs.com/package/@rjsf/material-ui
-[product-screenshots]: 
-- https://raw.githubusercontent.com/rjsf-team/react-jsonschema-form/59a8206e148474bea854bbb004f624143fbcbac8/packages/material-ui/screenshot.png
-- https://raw.githubusercontent.com/rjsf-team/react-jsonschema-form/59a8206e148474bea854bbb004f624143fbcbac8/packages/material-ui/screenshot5.png
+[product-screenshot]: https://raw.githubusercontent.com/rjsf-team/react-jsonschema-form/e2e1181d1020f18cad0c80c661ddae28edb9794e/packages/material-ui/screenshot5.png