Update official Ingress resource link (#3864)

docs: Update official Ingress resource link

At some stage the official Kubernetes documentation changed their
information architecture, leading to a broken link from the Overview
page of the NGINX Ingress Controller documentation.

There may be other instances of broken links from this change, which
will be addressed as they are discovered.

docs/content/intro/overview.md

@@ -21,7 +21,7 @@ The Ingress resource supports the following features:
     * *Path-based routing*. For example, routing requests with the URI that starts with `/serviceA` to service A and requests with the URI that starts with `/serviceB` to service B.
 * **TLS/SSL termination** for each hostname, such as `foo.example.com`.
 
-See the [Ingress User Guide](https://kubernetes.io/docs/user-guide/ingress/) to learn more about the Ingress resource.
+See the [Ingress Reference Documentation](https://kubernetes.io/docs/concepts/services-networking/ingress/) to learn more about the Ingress resource.
 
 ## What is the Ingress Controller?