Elaborate on Auth username format

For the setup step:
> Run the following command from your host shell replacing [AA USERNAME HERE] with your username.

I had to do some guessing and checking to figure out the format. Might want to elaborate that your `AA USERNAME HERE` is the name of the character you used to login with SSO *with the spaces replaced with underscores*. Ended up only figuring this out after running across the username field restrictions [here](https://docs.djangoproject.com/en/5.0/ref/contrib/auth/).