readme: remove legacy doc

Author: flomonster

.devcontainer/Dockerfile

@@ -40,22 +40,6 @@ docker run --rm -it -v $(pwd):/src -p 1313:1313 klakegg/hugo:ext-alpine server
 docker run --rm -it -v $(pwd):/src klakegg/hugo:ext-alpine
 ```
 
-### Gitpod
-
-Click the button below to start a new development environment using Gitpod :
-
-[![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/from-referrer/)
-
-### Devcontainer
-
-You can use devcontainer to run this website.
-Please read [documentation](https://code.visualstudio.com/docs/remote/create-dev-container) before.
-
-### Codespace
-
-You can use [Codespace](https://fr.github.com/features/codespaces) based on devcontainer to set up a remote development environment and run this website.
-For french developers Codespace is still in [beta](https://fr.github.com/features/codespaces).
-
 ## Contributing
 
 If you think OSRD doesn't quite fit your needs yet, but still believe it could,