[WIP] Newsletter bundle

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| Fixed tickets | 
| License       | MIT
| Doc PR        | Sylius/Sylius-Docs#218
can you provide some draft at least here? I can take that and PR the documentation if you want me to and when i get a chance. I would like to start improving a bit the docu.