message: add releasing instructions
diff: @@ -11,5 +11,9 @@ To build this into a full, usable library, see the [Analytics.js](https://github
  Released under the [MIT license](License.md).
  -
  [analytics.js]: https://segment.com/docs/libraries/analytics.js/
  +
  +## Releasing
  +
  +1. Update the version in `package.json`.
  +2. Run `robo release x.y.z` where `x.y.z` is the new version.
  