Describe release process

[pavolloffay]

Currently, the repository is missing a readme file describing release process.

[yurishkuro]

The mechanics of the release are simple and easy to describe:

1. Create a PR "Preparing release X.Y.Z" with an update to CHANGELOG.md, e.g. Preparing release 0.7.0 #351
2. After the PR is merged, create a Release on GitHub with a tag vX.Y.Z (must have v prefix) and the description copied from the changelog, e.g. v0.7.0
3. The tag will trigger a build of the docker images
4. Once the images are available on DockerHub, announce the release on the mailing list, gitter, and twitter

However, we don't have a formal process of deciding on the releases.

[pavolloffay]

A readme file with this would be good. Do we also plan to use other distribution channels? Like upload binaries to github releases? It might be useful for all-in-one. Users would just curl the binary and run it.