message: add create migration instructions
diff: @@ -48,6 +48,11 @@ To redo the last migration (i.e. down + up):
  `yarn db:migrate redo`
  +## Creating database migrations
  +`yarn db:migrate create <migration-name>`
  +
  +Documentation on how to create migration scripts is available at https://salsita.github.io/node-pg-migrate/#/migrations
  +
  ## Loading database seed data
  `yarn db:seed`
  