Documented the characters that provoke a YAML escaping string

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed tickets | #4197
technically, you can use double quotes all the time if you want. But it makes the escaping harder, because you need to escape ``\`` in it (because of control sequences) instead of just escaping single quotes