Update cluster docs based on feedback

Small changes for clarity in the cluster documentation.

doc/user/instance/clusters/index.md

@@ -12,8 +12,7 @@ projects.
 
 ## Cluster precedence
 
-GitLab will try [to match](../../../ci/environments/index.md#scoping-environments-with-specs) clusters in
-the following order:
+GitLab will try to match clusters in the following order:
 
 - Project-level clusters.
 - Group-level clusters.

doc/user/project/clusters/add_eks_clusters.md

@@ -148,7 +148,7 @@ To create and add a new Kubernetes cluster to your project, group, or instance:
    - **VPC** - Select a [VPC](https://docs.aws.amazon.com/vpc/latest/userguide/what-is-amazon-vpc.html)
      to use for your EKS Cluster resources.
    - **Subnets** - Choose the [subnets](https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Subnets.html)
-     in your VPC where your worker nodes will run.
+     in your VPC where your worker nodes will run. You must select at least two.
    - **Security group** - Choose the [security group](https://docs.aws.amazon.com/vpc/latest/userguide/VPC_SecurityGroups.html)
      to apply to the EKS-managed Elastic Network Interfaces that are created in your worker node subnets.
    - **Instance type** - The [instance type](https://aws.amazon.com/ec2/instance-types/) of your worker nodes.

doc/user/project/clusters/add_gke_clusters.md

@@ -24,8 +24,6 @@ requirements are met:
 Starting from [GitLab 12.4](https://gitlab.com/gitlab-org/gitlab/-/issues/25925), all the GKE clusters
 provisioned by GitLab are [VPC-native](https://cloud.google.com/kubernetes-engine/docs/how-to/alias-ips).
 
-### Important notes
-
 Note the following:
 
 - The [Google authentication integration](../../../integration/google.md) must be enabled in GitLab
@@ -38,9 +36,10 @@ Note the following:
   cluster's pod address IP range will be set to /16 instead of the regular /14. /16 is a CIDR
   notation.
 - GitLab requires basic authentication enabled and a client certificate issued for the cluster to
-  set up an [initial service account](add_remove_clusters.md#access-controls). Starting from [GitLab
-  11.10](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/58208), the cluster creation process will
-  explicitly request that basic authentication and client certificate is enabled.
+  set up an [initial service account](add_remove_clusters.md#access-controls). In [GitLab versions
+  11.10 and later](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/58208), the cluster creation process
+  explicitly requests GKE to create clusters with basic authentication enabled and a client
+  certificate.
 
 ### Creating the cluster on GKE