Update description to match other official providers (#699)
Update description to match other official providers (#699)

See:
- https://github.com/terraform-providers/terraform-provider-google/blob/master/README.md#terraform-provider-for-google-cloud-platform
- https://github.com/terraform-providers/terraform-provider-helm/blob/master/README.md#terraform-provider-for-helm
- https://github.com/terraform-providers/terraform-provider-azurerm/blob/master/README.md#terraform-provider-for-azure-resource-manager
terraform-providers/terraform-provider-kubernetes,terraform-providers/terraform-provider-kubernetes,terraform-providers/terraform-provider-kubernetes