Merge pull request #60454 from erictune/update-sample-apiserver-readme

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Update README.md of sample-apiserver.

Mention CRDs as option.
Link to CRD vs Aggr. docs.
Mention apiserver-builder as alternative.

```release-note
NONE
```

Kubernetes-commit: 04634cb19843195a43d13975d2a13d721512bb1d

README.md

@@ -5,7 +5,13 @@ Demonstration of how to use the k8s.io/apiserver library to build a functional A
 
 ## Purpose
 
-This is intended as an example of how to build a kube-like API server with a single type.
+You may use this code if you want to build an Extension API Server to use with API Aggregation, or to build a stand-alone Kubernetes-style API server.
+
+However, consider two other options:
+  * **CRDs**:  if you just want to add a resource to your kubernetes cluster, then consider using Custom Resource Definition a.k.a CRDs.  They require less coding and rebasing.  Read about the differences between Custom Resource Definitions vs Extension API Servers [here](https://kubernetes.io/docs/concepts/api-extension/custom-resources).
+  * **Apiserver-builder**: If you want to build an Extension API server, consider using [apiserver-builder](https://github.com/kubernetes-incubator/apiserver-builder) instead of this repo.  The Apiserver-builder is a complete framework for generating the apiserver, client libraries, and the installation program.
+
+If you do decide to use this repository, then the recommended pattern is to fork this repository, modify it to add your types, and then periodically rebase your changes on top of this repo, to pick up improvements and bug fixes to the apiserver.
 
 
 ## Compatibility