Document how to take a DB dump from a whitelisted IP address

[markfinger]

Re: https://github.com/ic-labs/django-icekit/issues/142#issuecomment-260499969

[mrmachine]

@markfinger In brief:

• Ensure your static IP is whitelisted (allows all traffic) by the Docker Cloud security group in the AWS management console
• PGHOST={host}.rds.amazonaws.com PGPASSWORD={password} PGUSER={username} pg_dump -O -v -x -f "/opt/{project}/initial_data.sql" {database}

OR

• Set the SRC_PG* environment variables in your .env.local file to pipe directly from the remote database when creating a new local database (e.g. when switching branches)