Documentation audit for array-helper feature flag

[tomdale]

We would like to "go" the array-helper feature flag that landed in canary.

We would like to request a Learning Team audit of the API docs as implemented today, as well as thoughts on whether the guides should be updated to cover this functionality.

[locks]

The documentation is already written at #212.

[jenweber]

closed by #177

It's in the guides as of the launch of 3.6 🎉