Watching additional sql files (referenced in afterCurrent)

### Summary

In the project I work on, we have a "seed.sql" included in `afterCurrent` field of the `.gmrc` config file.

The seed.sql contains testing data that I need to edit from time to time. When I edit it, and I have `graphile-migrate watch` running, it would be very handy if the current migration run again (like if the current migration was edited), and the seed data updated in database. My workaround is to actually edit the current migration by adding "select 1" there and then removing it :)

Is there a way to specify that `watch` command should also watch some additional files?

If there isn't a way, would it be a good opportunity for me to try to add it and submit PR?