Specify that Rancher provider is for 1.x only

docs/content/providers/rancher.md

@@ -1,12 +1,17 @@
 # Traefik & Rancher
 
-A Story of Labels, Services & Container
+A Story of Labels, Services & Containers
 {: .subtitle }
 
 ![Rancher](../assets/img/providers/rancher.png)
 
 Attach labels to your services and let Traefik do the rest!
 
+!!! important
+    This provider is specific to Rancher 1.x.
+    Rancher 2.x requires Kubernetes and does not have a metadata endpoint of its own for Traefik to query.
+    As such, Rancher 2.x users should utilize the [Kubernetes provider](./kubernetes-crd.md) directly.
+
 ## Configuration Examples
 
 ??? example "Configuring Rancher & Deploying / Exposing Services"