docs(readme): add link to the contribution guidelines (#241)

* Add link to the contribution guidelines in the README

* Update README.md

Co-authored-by: Kenji Miyake <31987104+kenji-miyake@users.noreply.github.com>

Co-authored-by: Kenji Miyake <31987104+kenji-miyake@users.noreply.github.com>

Author: maxime-clem

README.md

@@ -1,5 +1,9 @@
-# autoware-documentation
+# Autoware documentation
 
 - This repository contains the [MkDocs](https://www.mkdocs.org/) source files for the [Autoware documentation hosted on GitHub Pages](https://autowarefoundation.github.io/autoware-documentation/main/).
 - Since Autoware is made up of [multiple repositories](https://github.com/autowarefoundation/), a central documentation repository is important to make information accessible from a single place.
 - For more information about Autoware and its related repositories, refer to the [Autoware Foundation's organization profile](https://github.com/autowarefoundation/.github/blob/main/profile/README.md).
+
+## Contributions
+
+To contribute to this repository, see the [documentation guidelines](https://autowarefoundation.github.io/autoware-documentation/main/contributing/documentation-guidelines/).