Document how to append a value to a reference field

Started playing with a few options in DrupalPod but decided to move to my local to see if I can solve my personal issue.

Not all my personal issues... that's too much to ask

I recently had to import terms into a vocabulary with a custom field, allowing multiple terms from the source below. After searching I found this page, and eventually managed to get it to work. Maybe it can help someone else?

[
{
  "cities": [
  {
    "city_name": "The first city",
    "city_info": "Some info text"
  },
  {
    "city_name": "Another city",
    "city_info": "Another info text"
  }],
[...]

The import:

source:
  fields:
    -
      name: cities
      selector: cities
[...]
process:
  taxonomy_vocabulary_4:
    plugin: sub_process
    source: cities
    process:
      target_id:
        plugin: entity_generate
        source: city_name
        value_key: name
        bundle_key: vid
        bundle: vocabulary_4
        entity_type: taxonomy_term
        values:
          field_city_info/value: city_info