Docs: Changing the postgres credentials

docs/postgresql-setup.md

@@ -53,3 +53,22 @@ postgres=# SELECT version();
  PostgreSQL 18.6 (Ubuntu 18.6-0ubuntu0.26.04.1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 15.2.0-16ubuntu1) 15.2.0, 64-bit
 ```
 
+## Changing Postgres user password
+
+Since `PostgreSQL` runs under the `postgres` user, we need to use that user to access the database. By default, this user has no password, but by running the following command, we add a password.
+
+```txt
+user@it2810-11:~$ sudo passwd postgres
+[sudo: authenticate] Password:                                 
+Enter new password: 
+Retype new password: 
+Retype new password: 
+passwd: password updated successfully
+user@it2810-11:~$ 
+```
+
+Setting the password on the postgres instance itself is done with the following command
+
+```txt
+sudo -u postgres psql -c "ALTER USER postgres WITH PASSWORD 'super-secret-password-that-you-cant-read';"
+```