add a screenshot for the readme

README.md

-**Beyond-SI Landing page**
+# Beyond-SI Landing page
 
-Built from bootstrap template from [startbootstrap.com](https://startbootstrap.com/theme/landing-page). [MIT License applied](https://github.com/startbootstrap/startbootstrap-landing-page/blob/master/LICENSE).
+Built thank to bootstrap template from [**startbootstrap.com**](https://startbootstrap.com/theme/landing-page) ! 
+
+[MIT License applied](https://github.com/startbootstrap/startbootstrap-landing-page/blob/master/LICENSE).
+
+![landingpage-screenshot](readme_img/landingpage-screenshot.png)
+
+## Deployment and Maintenance
 
-**Deployment and Maintenance**
 To deploy this small web site, please use the following repository [beyond-si](https://forgemia.inra.fr/beyond/beyond_si)
 
+