Improve setup instructions and flow

[jwld]

Hello!

Had a bit of trouble getting set up locally:

• Connection string is commented out

  week6-BGJK/src/db/connection.js

  Line 8 in 93fb080

  // connectionString: process.env.DATABASE_URL

• It also doesn't match the name for the env variable given in the readme
• There was no easy way to call your build helper for the DB (easy to forget once you've already built it locally while deving !) - might be nice to have a script to do that

  week6-BGJK/package.json

  Lines 9 to 13 in 93fb080

  	"scripts": {
  	"test": "PGDATABASE=cookie_test tape test/test.js | tap-spec",
  	"start": "node src/server.js",
  	"dev": "nodemon src/server.js"
  	},