Update documentation

Scally also offers two additional layout utilities located in [utilities](../utilities/). The [**Side by Side** utility](../utilities/_u-side-by-side.scss) and [**Side by Side Alt](../utilities/_u-side-by-side-alt.scss) apply an extremely common UI layout pattern. *This will be moved to the layout section, [see](https://github.com/westfieldlabs/scally/issues/153)*.