Updated env instructions based on PostgreSQL issues

@mathemagica Can you please review these env instructions changes?
I was getting that error pretty consistently on my machine. For some reason, the Unix domain socket was not able to use localhost until I added that env variable.

I suspect the missing env variable was also the root cause of the missing variable `PGDATA` error I was getting.

If no one else experienced this error, feel free to take the instructions out, because a quick Google search returns the env variable suggestion.