Update CONTRIBUTING.md to contain all information in one place

CONTRIBUTING.md

@@ -2,8 +2,10 @@
 
 Here are some guidelines that should help to start contributing to the project.
 
-- [Submitting pull Requests](https://github.com/traefik/contributors-guide/blob/master/pr_guidelines.md)
+- [Submitting pull Requests](https://doc.traefik.io/traefik/contributing/submitting-pull-requests/)
 - [Submitting issues](https://doc.traefik.io/traefik/contributing/submitting-issues/)
-- [Submitting security issues](docs/content/contributing/submitting-security-issues.md)
+- [Submitting security issues](https://doc.traefik.io/traefik/contributing/submitting-security-issues/)
+- [Advocating for Traefik](https://doc.traefik.io/traefik/contributing/advocating/)
+- [Triage Process](https://github.com/traefik/contributors-guide/blob/master/issue_triage.md)
 
 If you are willing to become a maintainer of the project, please take a look at the [maintainers guidelines](docs/content/contributing/maintainers-guidelines.md).