Merge pull request #57572 from sttts/sttts-move-metrics-md

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>.

metrics: make IMPLEMENTATIONS.md and CONTRIBUTING.md authorative in k/k

Part of https://github.com/kubernetes/kubernetes/issues/57559.

staging/src/k8s.io/metrics/CONTRIBUTING.md

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+# Contributing guidelines
+
+## How to become a contributor and submit your own code
+
+### Contributor License Agreements
+
+We'd love to accept your patches! Before we can take them, we have to jump a couple of legal hurdles.
+
+Please fill out either the individual or corporate Contributor License Agreement (CLA).
+
+  * If you are an individual writing original source code and you're sure you own the intellectual property, then you'll need to sign an [individual CLA](https://identity.linuxfoundation.org/node/285/node/285/individual-signup).
+  * If you work for a company that wants to allow you to contribute your work, then you'll need to sign a [corporate CLA](https://identity.linuxfoundation.org/node/285/organization-signup).
+
+Follow either of the two links above to access the appropriate CLA and instructions for how to sign and return it. Once we receive it, we'll be able to accept your pull requests.
+
+### Contributing A Patch
+
+1. Submit an issue describing your proposed change to the repo in question.
+1. The [repo owners](OWNERS) will respond to your issue promptly.
+1. If your proposed change is accepted, and you haven't already done so, sign a Contributor License Agreement (see details above).
+1. Fork the desired repo, develop and test your code changes.
+1. Submit a pull request.
+
+### Adding dependencies
+
+If your patch depends on new packages, add that package with [`godep`](https://github.com/tools/godep). Follow the [instructions to add a dependency](https://github.com/kubernetes/kubernetes/blob/master/docs/devel/development.md#godep-and-dependency-management).

staging/src/k8s.io/metrics/IMPLEMENTATIONS.md

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+# Implementations
+
+## Resource Metrics API
+
+- [Heapster](https://github.com/kubernetes/heapster): a application which
+  gathers metrics, writes them to metrics storage "sinks", and exposes the
+  resource metrics API from in-memory storage.
+
+- [Metrics Server](https://github.com/kubernetes-incubator/metrics-server):
+  a lighter-weight in-memory server specifically for the resource metrics
+  API.
+
+## Custom Metrics API
+
+***NB: None of the below implemenations are officially part of Kubernetes.
+They are listed here for convenience.***
+
+- [Prometheus
+  Adapter](https://github.com/directxman12/k8s-prometheus-adapter).  An
+  implementation of the custom metrics API that attempts to support
+  arbitrary metrics following a set label and naming scheme.
+
+- [Google Stackdriver (coming
+  soon)](https://github.com/GoogleCloudPlatform/k8s-stackdriver)