docs: update README to warn about master branch

README.md

@@ -1,6 +1,14 @@
 # etcd
 
-README version 0.4.6
+## WARNING ##
+
+The current `master` branch of etcd is under heavy development in anticipation of the forthcoming 0.5.0 release. 
+
+It is strongly recommended that users work with the latest 0.4.x release (0.4.6), which can be found on the [releases](https://github.com/coreos/etcd/releases) page.
+
+Unless otherwise noted, the etcd documentation refers to configuring and running 0.4.x releases.
+
+## README version 0.4.6
 
 A highly-available key value store for shared configuration and service discovery.
 etcd is inspired by [Apache ZooKeeper][zookeeper] and [doozer][doozer], with a focus on being:
@@ -47,12 +55,6 @@ _NOTE_: etcd requires go 1.2+. Please check your installation with
 go version
 ```
 
-See the [development tools documentation][development-tools] for alternative build methods like using Vagrant.
-
-[development-tools]: https://github.com/coreos/etcd/blob/master/Documentation/development-tools.md
-
-### Running
-
 First start a single-machine cluster of etcd:
 
 ```sh
@@ -124,9 +126,9 @@ The `v1` API has been deprecated and will not be supported.
 
 During the pre-v1.0.0 series of releases we may break the API as we fix bugs and get feedback.
 
-#### 32bit systems
+#### 32-bit systems
 
-etcd has known issues on 32bit systems. We plan to address these issues after the 0.4 release.
+etcd has known issues on 32-bit systems.
 
 ### License