add changelog

Signed-off-by: Victor Vieux <vieux@docker.com>

CHANGELOG.md

@@ -0,0 +1,36 @@
+# Changelog
+
+## 0.4 (2015-08-04)
+
+#### Scheduler
+
+- Reschedule with soft affinity when image cannot be pulled
+
+#### Store
+
+- Replace the store pkg by libKV
+- Fixes about consul/etcd and zookeeper
+
+#### API
+
+- Fix docker push name matching
+- Fix docker exec status code
+- Fix docker pull status code
+
+#### Docker Engine Compatibility
+
+- Improve docker info with docker client 1.7.x
+- Add SystemTime, http_proxy, https_proxy and no_proxy to docker info
+
+#### Mesos integration
+
+- Task creation timeout configurable
+- Fix issue with hostname in library image
+- Use 'docker_port' attribute if available
+- Add support for random ports
+
+#### Misc
+
+- Add doc on leader election / high availability of swarm manager
+- Lots of typos/improvements to the doc
+- Switch to golang 1.4