🐛(readme) fix preprod link to redirect to homepage (#747)

The current link redirects to a 404. New link redirect to homepage.

Author: virgile-dev

README.md

@@ -46,7 +46,7 @@ Docs is a collaborative text editor designed to address common challenges in kno
 
 ### Test it
 
-Test Docs on your browser by logging in on this [environment](https://impress-preprod.beta.numerique.gouv.fr/docs/0aa856e9-da41-4d59-b73d-a61cb2c1245f/)
+Test Docs on your browser by logging in on this [environment](https://impress-preprod.beta.numerique.gouv.fr/)
 
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 email: [email protected]