Constructing mutable arrays: improve docs

When encountering the documentation for Constructing mutable arrays I was somewhat frustrated that the meaning of the tuple argument was not specified.

This merge request seeks to avoid this frustration for future Haskellers.

Thanks for your patch, it's really frustrated for new comers who is not familiar with Ix class!

Do you have a chance to do a rebase before it is merged?

It surprises me that we cannot rebase MR from UI directly in gitlab, much like we could do in github...

mentioned in merge request !19 (merged)

Close in favor of !19 (merged)

closed