README refers to non-existent files

The README in uswds_gulp_subtheme says...

7. Update the path for images in `_uswds-theme-general.scss` to be
`../assets/img`
8. Update the path for fonts in `_uswds-theme-typography.scss` to be
`../assets/fonts`

However, the above two scss files do not exist anywhere in the subtheme.