Use md extension instead of html

doc/user/project/clusters/add_eks_clusters.md

@@ -141,7 +141,7 @@ To create and add a new Kubernetes cluster to your project, group, or instance:
 1. Choose your cluster's settings:
    - **Kubernetes cluster name** - The name you wish to give the cluster.
    - **Environment scope** - The [associated environment](index.md#setting-the-environment-scope) to this cluster.
-   - **Kubernetes version** - The [Kubernetes version](index.html#supported-cluster-versions) to use.
+   - **Kubernetes version** - The [Kubernetes version](index.md#supported-cluster-versions) to use.
    - **Service role** - Select the **EKS IAM role** you created earlier to allow Amazon EKS
      and the Kubernetes control plane to manage AWS resources on your behalf.