Added standard bundle installation instructions

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | -
| Fixed tickets | #4157

Note: if you think that this draft is awful, please say it so and we'll rewrite it from scratch.
If we add the return statements, I don't think that this is necessary. Usually you would simply add the new bundle at the end of the array and then return the ``$bundles`` array, won't you? So, having another placeholder there might lead to some confusion.