fix(docs) : Fixing the environment variable & Vercel Deployment Build command

[ayushpattnaik]

There are two changes to the documentation:

1. Environment Variable name mismatch between code and Vercel

The neon-managed vercel integration automatically sets the environment variables in Vercel like this :

So the build fails because it is not able to detect the DIRECT_URL variable and hence fails to find datasource.url

Therefore it is safe to change it to DATABASE_URL_UNPOOLED since for other deployment platforms there would be no such auto env variable naming. And if there is, we might need to change from vercel part of the code to give correct variable names

2. Pre-requisite command for Vercel Build

Current command for build override (npx prisma migrate deploy && npm run build) fails because it is not able to detect the client from the generated schema folder because there is no schema generate without theprisma generatecommand.

[vercel]

@ayushpattnaik is attempting to deploy a commit to the neondatabase Team on Vercel.

A member of the Team first needs to authorize it.