Replace the wiki link which now points to this file - a loop

Signed-off-by: Viet Hung Nguyen <hvn@familug.org>

CONTRIBUTING.md

@@ -26,7 +26,7 @@ When requesting or submitting new features, first consider whether it might be u
 
 - Check the codebase to ensure that your feature doesn't already exist.
 - Check the pull requests to ensure that another person hasn't already submitted the feature or fix.
-- Read and understand the [DCO guidelines](https://github.com/pi-hole/pi-hole/wiki/Contributing-to-the-project) for the project.
+- Read and understand the [DCO guidelines](https://docs.pi-hole.net/guides/github/contributing/) for the project.
 
 ## Technical Requirements