Consider to support deployment step

[jelhan]

I noticed that some adopted ember addons have a custom deployment step at the end of their pipeline:

• ember-autoresize: https://github.com/adopted-ember-addons/ember-autoresize/blob/e1d172f69c89772a5d48dabf340335e932a09619/.travis.yml#L47-L50
• ember-collapsile-panel: https://github.com/adopted-ember-addons/ember-collapsible-panel/blob/e6bc55477761df5d57de5981c9d97c5ffb5c632c/.travis.yml#L33-L40

This is a similar use case as having a code coverage check, which is tracked in #40. But while it's quiet clear that code coverage belongs to CI, I'm actually not that sure for deployment. Unless the version is also released in the CI pipeline, one might argue that the docs for a released version should be deployed regardless if CI passes or not. Especially if that CI does not verify the documentation app itself. In that case a separate workflow might be better.