atc/steps: update comment about StepWrapper's
Words are hard.
This comment should help clarify what is expected of the Wrap() function
in this interface. Someone can also look at existing StepWrapper's like
RetryStep.
@@ -172,8 +172,8 @@ type StepWrapper interface {
// Wrap is called during (Step).UnmarshalJSON whenever an 'inner' step is
// parsed.
//
- // Modifier step types should implement this by assigning a `json:"-"` tag to
- // an internal field of type StepConfig in their struct.
+ // Modifier step types should implement this function by assigning to an
+ // internal field, that has a `json:"-"` tag, the passed in StepConfig.
Wrap(StepConfig)
// Unwrap is called during (Step).MarshalJSON and must return the wrapped
