Create a dump and write documentation for loading the dump for local development

[hancush]

Running the scrapers is a perennial barrier to local development, in particular for new team members. Let's create a dump from the canned scrape (docker-compose run --rm scrapers, then pg_dump -Fc -O -h localhost -p 32001 -d lametro > dev.dump, and update the README with instructions on restoring a dump for development.

Here's an example of documentation! https://github.com/datamade/bga-payroll#restore-from-a-database-dump

[antidipyramid]

Now that we're on Heroku, it's much easier to dump the staging/live databases and load them locally.

https://devcenter.heroku.com/articles/heroku-postgres-backups