Document how GEOMETRY is used

[ephys]

The only reference to postgis in our documentation is this.

We should document how these misc types are used (hstore, geography, geometry), and check whether they are different in mysql and postgres

Here is a resource @Pihentagy shared on slack that can help:

https://stackoverflow.com/questions/32059758/how-to-insert-a-postgis-geometry-point-in-sequelize-orm