readme: add contributing file + fix outdated links

Signed-off-by: Ethan Perruzza <ethan.perruzza@gmail.com>

CONTRIBUTING.md

@@ -0,0 +1,37 @@
+# Contributing to OSRD
+
+All contributions, bug reports, bug fixes, documentation improvements,
+enhancements, and ideas are welcome.
+
+Check out our community's [Code of Conduct](https://github.com/OpenRailAssociation/osrd/blob/dev/CODE_OF_CONDUCT.md)
+and feel free to say hi on our [#public-general:osrd.fr](https://matrix.to/#/#public-general:osrd.fr)
+matrix channel if you'd like. It's a nice place to chat about OSRD development,
+ask questions, and get to know the other contributors and users in a less formal
+setting.
+
+## Getting oriented
+
+The OSRD project has 2 primary repos:
+
+1. [`osrd`](https://github.com/OpenRailAssociation/osrd): This is where the
+simulator is developed.
+2. [`osrd-website`](https://github.com/OpenRailAssociation/osrd-website): Where
+the [`official website`](https://osrd.fr), blog, documentation, ... are hosted.
+
+This is the website repo. For more info on the project or to contribute to the
+project itself checkout the [Contributing](https://github.com/OpenRailAssociation/osrd/blob/dev/CONTRIBUTING.md)
+file of the main repo.
+
+## Contribute code
+
+To comply with the [DCO](http://developercertificate.org/), all commits must
+include a Signed-off-by line. You can find more information about this here:
+[osrd.fr/docs/guides/contribute/contribute-code/commit-style/#the-developer-certificate-of-origin](https://osrd.fr/en/docs/guides/contribute/contribute-code/commit-style/#the-developer-certificate-of-origin)
+
+### Pull request / code review
+
+[osrd.fr/docs/contribute/code/#share-your-changes](https://osrd.fr/en/docs/guides/contribute/code/#share-your-changes).
+
+### Report and solve bugs
+
+[osrd.fr/docs/contribute/bug-reports](https://osrd.fr/en/docs/guides/contribute/bug-reports)

README.md

@@ -44,12 +44,13 @@ docker run --rm -it \
 ## Contributing
 
 If you think OSRD doesn't quite fit your needs yet, but still believe it could,
-please [tell us about your needs](https://github.com/osrd-project/osrd/issues/new).
+please [tell us about your needs](https://github.com/OpenRailAssociation/osrd/issues/new?labels=kind%3Aquestion&template=question.yaml).
 
 Please consider committing resources to help development if you'd like to use OSRD in production.
 Code contributions are very welcome, and we'd love to work together to make this project better.
 
+For more information on how to contribute, check out the [Contributing file](./CONTRIBUTING.md)
 
-## Contact
+## Get in touch
 
-You are interested in the project, and you want to know more? Contact us at <contact@osrd.fr>.
+Send an email at <contact@osrd.fr>, [open an issue](https://github.com/OpenRailAssociation/osrd-website/issues/new), or join the [#public-general:osrd.fr](https://matrix.to/#/#public-general:osrd.fr) matrix channel.