Minor error in backgrounds article

[vickychijwani]

Hi, thanks for your work on this! I think it'll grow to be a great resource for the community.

I found a minor error on the backgrounds article, the "left" and "right" are switched (error marked in bold below):

It is actually quite difficult to see these constraints if we do them all at once, so let’s look at them side by side and focus on how we constrain the verticals of the background view (on the left) to the visual children (on the right):