Dump n load instructions

[louispt1]

Context

Extend myetm readme to cover local database set up and import-scenarios usage.

Implemented changes

Extended the readme to outline:

• How to set up a new local db from scratch
• How to use the bin/import-scenarios command to import scenarios from beta/pro locally

Checklist

• [~] I have tested these changes (sort of, not from scratch)
• I have updated documentation as needed
• I have tagged the relevant people for review

The truest way to test this is by turning dbbot off except for ETLocal, and to test the instructions with a new employee who is setting up for the first time.
Alternatively someone could spend some time dropping all their local dbs and testing the set up from scratch.

@aaccensi I tagged you in case you can spot something I've missed
@mabijkerk I tagged you for functional review - feel free to reassign if you think someone else would be better suited or has more time

[aaccensi]

Overall the process is good. I only saw:

• A few text references that are not the actual exact labels.
• A couple of clarifications regarding what the scenarios in the import contain.

[louispt1]

Overall the process is good. I only saw:

* A few text references that are not the actual exact labels.

* A couple of clarifications regarding what the scenarios in the import contain.

Thanks for looking this over @aaccensi! I've processed the suggestions