README: Update obsolete link

docs/getting-started-guides/docker.md

-This file has moved to: https://github.com/kubernetes/kubernetes/blob/master/docs/devel/local-cluster/docker.md
+This file has moved to [https://github.com/kubernetes/community/blob/master/contributors/devel/local-cluster/docker.md](https://github.com/kubernetes/community/blob/master/contributors/devel/local-cluster/docker.md)
 
 
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