(Examples - Databases - PostgreSQL) Add more info about configuring the database (#2156)

## Summary

I was struggling to configure postgresql with Phoenix Framework because
of the lack of instructions, so I figured it out and am adding the
information that solved my problem.

## How was it tested?

I've tested on terminal and using the Phoenix Framework to create the
database.

Signed-off-by: Rafael <[email protected]>

Author: rafaelfess

docs/app/docs/devbox_examples/databases/postgres.md

@@ -41,7 +41,29 @@ You can use `devbox services start|stop postgresql` to start or stop the Postgre
 
 This variable tells PostgreSQL which directory to use for creating and storing databases.
 
-### Notes
+### NOTES
 
-To initialize PostgreSQL run `initdb`. You also need to create a database using `createdb <db-name>`
+1. To initialize PostgreSQL run:
+```sh
+initdb
+```
+3. You also need to create a user using:
+```sh
+createuser --interactive
+```
+5. (OPTIONAL) If the user has no permissions to create or drop a database, you also need to create a database using:
+```sh
+createdb <db-name>
+```
+
+#### Using the `createuser` Command
+
+Run the createuser command with the `-s` or `--superuser` option to create a superuser. This grants the user the ability to bypass all access permission checks within the database, effectively granting them extensive privileges including the ability to create and drop databases. Additionally, you can use the `-r` or `--createrole` option to allow the user to create new roles. Here's an example command:
+
+```sh
+createuser -s -r your_new_user_name
+```
+
+Replace `your_new_user_name` with the desired username for the new superuser.
 
+Remember: Creating a superuser grants them significant power over the database system, so it should be done cautiously and only when absolutely necessary due to the potential security implications.