The documentation mentions an environment variable "DBHOST"
to configure the postgres database, but I believe pq
expects PGHOST (see https://www.postgresql.org/docs/current/libpq-envars.html

)

Update the README and command help text with env var PGHOST
and link to the relevant postgres documentation in the README.

Signed-off-by: Will Daly <will.e.daly@gmail.com>