Not clear what match_background=True does

`reproject_and_coadd` has the `match_background` option, but the docs for this are currently just `'Whether to match the backgrounds of the images.'` (https://reproject.readthedocs.io/en/stable/api/reproject.mosaicking.reproject_and_coadd.html).

From this it's not clear exactly what the effect of setting `match_background=True` is on each of the images that are being coadded, so it would be great to get an expanded description of this.

Start with the reproject_and_coadd API documentation linked in the issue and locate the current match_background parameter description. Clarify the effect of setting match_background=True on each image being coadded, then verify that the generated documentation explains the behavior more precisely.

Written by the indexing model from the issue text.