Use more succinct postgres role creation command

It is far less error prone to use the tools that Postgres provides to create the role and the database. This amendment also ensures the created role password is encrypted.

doc/database/postgres/configure-postgres.md

@@ -4,23 +4,10 @@ Configuring Postgres database
 These are instructions for setting up NNTPChan with Postgres as the data-storage system.
 
 ##Configuring Postgres
+A user with sufficient privileges to run su is required (hint: you can use root). This command switches to the Postgres user, creates a Postgres role called `srnd`, and prompts for a password. For illustrative purposes, we will use `srnd` as the password.
 
-Setting up postgres (as root):
+    # su - postgres -c "createuser --pwprompt --createdb --encrypted srnd"
-
-    # become postgres user
-    su postgres
-    # spawn postgres admin shell
-    psql 
-
-You'll get a prompt, enter the following:
-
-    CREATE ROLE srnd WITH LOGIN PASSWORD 'srnd';
-    CREATE DATABASE srnd WITH ENCODING 'UTF8' OWNER srnd;
-    \q
-
-For demo purposes we'll use these credentials.
-These are default values, please change them later.
 
 ###Important
 
-These credentials assume you are going to run using a user called `srnd`, if your username you plan to run the daemon as is different please change `srnd` to your username.
+It's easiest to connect to Postgres using role-based authentication. In this case, our Linux user `srnd` matches up with our Postgres role `srnd`, so role-based authentication can take place. If you're running SRNDv2 as a different user (e.g. `nntpchan`), you will need to create a role that matches that user using the command above.