Update postgresql.md

Changed `prisma` to `prisma2`

Update tutorial.md

the Prisma 2 CLI is installed using `npm install prisma2 -g` and thus will be available as `prisma2`

add SSL connection docs for postgres

Update upgrading-from-prisma-1.md

Update prisma schema file doc. User can already use .env file.

Update tutorial.md

Update tutorial.md

Update tutorial.md

Remove nullable lists from docs

Cli typo

Update introspection.md

Fix typo in tutorial.md