Enhance initial-setup README with additional Docker & PGAdmin instructions

[astro-ing]

Add additional steps complementing the existing Dimensional Data Modeling guide for setting up Postgres in Docker, including locating credentials to log in to PGAdmin, noting browser quirks, and walking through how to add a new server.

These steps were written for the community, and following positive feedback, I felt they should be included in the documentation.

[isangwanrahul]

We already have these steps written in more explained way in readme.

[astro-ing]

We already have these steps written in more explained way in readme.

@isangwanrahul Hey thanks for reviewing. Could you point to where please as I'm not seeing it. This PR complements the existing steps and unblocked at least several people in just one day, enabling them to complete setup, and will hopefully reduce future support requests.

[isangwanrahul]

I meant to say I don't see any significant change in the commit. It's just reordering and reformatting. Thanks.

[astro-ing]

I can see how it appears that way. However, starting the Postgres install section by directing to option 2 over 1 helps people use containers and are less likely to have custom issues. And whilst changed lines 84-90 are just reformatted, lines 92 onwards provide crucial additional detail for those struggling.