docs(upgrade): instructions for upgrade to v0.4

Documentation/upgrade.md

@@ -0,0 +1,17 @@
+# Upgrading an Existing Cluster
+
+etcd clusters can be upgraded by doing a rolling upgrade or all at once. We make every effort to test this process, but please be sure to backup your data [by etcd-dump](https://github.com/AaronO/etcd-dump), or make a copy of data directory beforehand.
+
+## Upgrade Process
+
+- Stop the old etcd processes
+- Upgrade the etcd binary
+- Restart the etcd instance using the original --name, --address, --peer-address and --data-dir.
+
+## Rolling Upgrade
+
+During an upgrade, etcd clusters are designed to continue working in a mix of old and new versions. It's recommended to converge on the new version quickly. Using new API features before the entire cluster has been upgraded is only supported as a best effort. Each instance's version can be found with `curl http://127.0.0.1:4001/version`.
+
+## All at Once
+
+If downtime is not an issue, the easiest way to upgrade your cluster is to shutdown all of the etcd instances and restart them with the new binary. The current state of the cluster is saved to disk and will be loaded into the cluster when it restarts.

README.md

@@ -81,6 +81,7 @@ You have successfully started an etcd on a single machine and written a key to t
 - Learn about the dashboard, lock and leader election [modules][modules].
 - Use TLS to [secure an etcd cluster][security].
 - [Tune etcd][tuning].
+- [Upgrade from old version][upgrade].
 
 [api]: https://github.com/coreos/etcd/blob/master/Documentation/api.md
 [clustering]: https://github.com/coreos/etcd/blob/master/Documentation/clustering.md
@@ -89,6 +90,7 @@ You have successfully started an etcd on a single machine and written a key to t
 [modules]: https://github.com/coreos/etcd/blob/master/Documentation/modules.md
 [security]: https://github.com/coreos/etcd/blob/master/Documentation/security.md
 [tuning]: https://github.com/coreos/etcd/blob/master/Documentation/tuning.md
+[upgrade]: https://github.com/coreos/etcd/blob/master/Documentation/upgrade.md
 
 ## Contact