Document Postgres requirement

[samueljsb]

The contributing guide does not mention the requirement to have a Postgres server running to run the tests. it should do!

[HamaBarhamou]

who is working on this ticket ? I may be able to look into the matter.
cc @samueljsb

[samueljsb]

Hi @HamaBarhamou, please do! We're keen to avoid documenting other tools in this project, so ideally we'd be able to mention the requirement and link to the Postgres docs for more details. Thanks 🙂