docs: fix ndctl link

Author: pohly

docs/design.md

@@ -40,7 +40,7 @@ based on where the storage device(s) are physically attached.
 
 <sup>3 </sup> **fsdax mode** is required for NVDIMM
 namespaces. See [Persistent Memory
-Programming](https://pmem.io/ndctl/ndctl-create-namespace.html) for
+Programming](https://docs.pmem.io/ndctl-user-guide/ndctl-man-pages/ndctl-create-namespace) for
 details. `devdax` mode is not supported. Though a
 raw block volume would be useful when a filesystem isn't needed, Kubernetes
 cannot handle [binding a character device to a loop device](https://github.com/kubernetes/kubernetes/blob/7c87b5fb55ca096c007c8739d4657a5a4e29fb09/pkg/volume/util/util.go#L531-L534).