docs: add contributing section to README

Author: LexLuengas

README.md

@@ -252,6 +252,11 @@ Read more information about the usage [here](./docker/README.md).
   Yes. This is a proxy and not a middleware. You can use it between whatever HTTP-endpoints you have in your architecture.
 </details>
 
+## Contributing
+
+If you want to contribute to openapi-cop, be sure to check the [Contributing guidelines](CONTRIBUTING.md) and
+the [Contributing](https://github.com/EXXETA/openapi-cop/wiki/Contributing) wiki page.
+
 * * *
 
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