Documenter le trigger à -1

ex:

```yml
identities:
  - sources: ['I', 'W']
    type: 'cycle'
    name: cycle-1
    rules: {
      'inetOrgPerson.departmentNumber': 'etd',
    }
    mutation: {
      'inetOrgPerson.cn': 'mutated',
    }

    trigger: -1
    dateKey: 'metadata.lastUpdatedAt'

    target: D

```