Add further instructions to setting up database without docker

[ethyl2]

It would be very helpful for students to have more steps documented for getting the database running without docker, for after postgres is installed.
Including:
2. How to create a new db in pgAdmin
3. How to update .env url variable.

[tinomen]

@ethyl2 would you be interested in submitting this guide as a markdown doc in examples to the new docs?

https://github.com/Lambda-School-Labs/gitbook-basic-api