README needs updating

[zkl94]

The current version still says:

1. gunzip stations.json.gz
2. mongoimport --host=<hostname> --port=<port> --username=<username> --password=<password> --db=<mydb> --collection=stations stations.json

even when the format has been changed to bson.

It would be better to update it to somthing like:

1. gunzip stations.bson.gz
2. bsondump stations.bson > stations.json
3. mongoimport --host=<hostname> --port=<port> --username=<username> --password=<password> --db=<mydb> --collection=stations stations.json