Un-prune code-generator scripts

Scripts under code-generator are required to generate code when
snapshot APIs are changed. Therefore they should not be pruned.

vendor/k8s.io/code-generator/README.md

@@ -0,0 +1,24 @@
+# code-generator
+
+Golang code-generators used to implement [Kubernetes-style API types](https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md).
+
+## Purpose
+
+These code-generators can be used
+- in the context of [CustomResourceDefinition](https://kubernetes.io/docs/tasks/access-kubernetes-api/extend-api-custom-resource-definitions/) to build native, versioned clients,
+  informers and other helpers
+- in the context of [User-provider API Servers](https://github.com/kubernetes/apiserver) to build conversions between internal and versioned types, defaulters, protobuf codecs,
+  internal and versioned clients and informers.
+
+## Resources
+- The example [sample controller](https://github.com/kubernetes/sample-controller) shows a code example of a controller that uses the clients, listers and informers generated by this library.
+- The article [Kubernetes Deep Dive: Code Generation for CustomResources](https://blog.openshift.com/kubernetes-deep-dive-code-generation-customresources/) gives a step by step instruction on how to use this library.
+
+## Compatibility
+
+HEAD of this repo will match HEAD of k8s.io/apiserver, k8s.io/apimachinery, and k8s.io/client-go.
+
+## Where does it come from?
+
+`code-generator` is synced from https://github.com/kubernetes/kubernetes/blob/master/staging/src/k8s.io/code-generator.
+Code changes are made in that location, merged into `k8s.io/kubernetes` and later synced here.