Reformat to Markdown, remove obsolete references, point users at website
Signed-off-by: Andrei Tatar <andrei@unikraft.io>
Reviewed-by: Maria Sfiraiala <maria.sfiraiala@gmail.com>
Reviewed-by: Stefan Jumarea <stefanjumarea02@gmail.com>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #15
-Contributing to Unikraft
-========================
+# Contributing to Unikraft
-Please refer to the `CONTRIBUTING.md` file in the main Unikraft repository.
+Contributions to Unikraft are welcome!
+Please refer to the [Contributing](https://unikraft.org/docs/contributing/) page for further information.