Update CONTRIBUTING.md

CONTRIBUTING.md

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-# How to contribute <a name="top"/>
+# How to contribute
 
-Please check our [contribution document](https://github.com/HumanBrainProject/openMINDS/blob/main/CONTRIBUTING.md).
+The openMINDS metadata framework is an open-source project and community contributions are highly appreciated. If you want to contribute please follow our :arrow_right: [**contribution guidelines**][contribution-url].
+
+<!-- MARKDOWN LINKS & IMAGES -->
+<!-- https://www.markdownguide.org/basic-syntax/#reference-style-links -->
+[contribution-url]: https://openminds-documentation.readthedocs.io/en/latest/shared/contribution_guidelines.html