Update user guide to have section on database setup

[simyilin]

Hello! I ran into some errors when following along the tutorial and these were what I did to fix them:

• Ensuring the database specified in databases.json exists in the local Postgres server (e.g. running 'CREATE DATABASE nodejs-starter-dev' command in psql shell)
• Adding username and password keys in databases.json
• Installing Sequelize CLI and applying migrations to create the 'Users' table (https://sequelize.org/master/manual/migrations.html)

I'm not sure if it was just me missing something but it feels like the guide would benefit from an additional step about database setup. Would appreciate any thoughts on this. Thanks!

[simyilin]

Sorry wrong repo!