Extract db config into environment variables by environment
Recommend db:migrate command over db:schema:load

Beginners will likely be more familiar with this task and since these
instructions are meant to be run at the start of the apps lifecycle
there is no risk of a break in the chain of defined migrations (the
reason db:schema:load would be preferred).
Heroku has made env var available on all builds

The user-env-compile addon is no longer needed with
the new buildpacks.

https://devcenter.heroku.com/changelog-items/416
Recommend running the command prefixed with `bundle exec`

to avoid possible dependency management issues