Clarify client-go issue location (kubernetes#85464)

* Clarify client-go issue location

While pull requests should be in kubernetes/kubernetes, it seems issues are
tracked in client-go repo.

* All Issues along with PRs (except README.md) should be opened in kubernetes/kubernetes

Author: coryrc

staging/src/k8s.io/client-go/CONTRIBUTING.md

@@ -1,6 +1,6 @@
 # Contributing guidelines
 
-Do not open pull requests directly against this repository, they will be ignored. Instead, please open pull requests against [kubernetes/kubernetes](https://git.k8s.io/kubernetes/).  Please follow the same [contributing guide](https://git.k8s.io/kubernetes/CONTRIBUTING.md) you would follow for any other pull request made to kubernetes/kubernetes.
+Do not open pull requests directly against kubernetes/client-go repository (except for README.md); they will be ignored. Instead, please open pull requests and issues against [kubernetes/kubernetes](https://git.k8s.io/kubernetes/).  Please follow the same [contributing guide](https://git.k8s.io/kubernetes/CONTRIBUTING.md) you would follow for any other pull request made to kubernetes/kubernetes.
 
 This repository is published from [kubernetes/kubernetes/staging/src/k8s.io/client-go](https://git.k8s.io/kubernetes/staging/src/k8s.io/client-go) by the [kubernetes publishing-bot](https://git.k8s.io/publishing-bot).