Documented the characters that provoke a YAML escaping string

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed tickets | #4197
I think it's confusing to put all these chars in a single line and separate them with a comma. You never know if the comma is a comma or a special char or part of other special char. That's why I used a table originally ;) In any case, tables, single-item lists or multiple-items lists all look awful to me in this case. I can't think of anything that makes this look OK.