Adding a README for federation API ref docs

federation/docs/api-reference/README.md

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+<h2>PLEASE NOTE: This document applies to the HEAD of the source tree</h2>
+
+If you are using a released version of Kubernetes, you should
+refer to the docs that go with that version.
+
+<!-- TAG RELEASE_LINK, added by the munger automatically -->
+<strong>
+The latest release of this document can be found
+[here](http://releases.k8s.io/release-1.4/federation/docs/api-reference/README.md).
+
+Documentation for other releases can be found at
+[releases.k8s.io](http://releases.k8s.io).
+</strong>
+--
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+
+# API Reference
+
+Federation API server supports the following group versions:
+
+* federation/v1beta1: [operations](https://htmlpreview.github.io/?https://github.com/kubernetes/kubernetes/blob/HEAD/federation/docs/api-reference/federation/v1beta1/operations.html), [model definitions](https://htmlpreview.github.io/?https://github.com/kubernetes/kubernetes/blob/HEAD/federation/docs/api-reference/federation/v1beta1/definitions.html)
+* v1: [operations](https://htmlpreview.github.io/?https://github.com/kubernetes/kubernetes/blob/HEAD/federation/docs/api-reference/v1/operations.html), [model definitions](https://htmlpreview.github.io/?https://github.com/kubernetes/kubernetes/blob/HEAD/federation/docs/api-reference/v1/definitions.html)
+* extensions/v1beta1: [operations](https://htmlpreview.github.io/?https://github.com/kubernetes/kubernetes/blob/HEAD/federation/docs/api-reference/extensions/v1beta1/operations.html), [model definitions](https://htmlpreview.github.io/?https://github.com/kubernetes/kubernetes/blob/HEAD/federation/docs/api-reference/extensions/v1beta1/definitions.html)
+
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