To answer my own question...

To add the NIP05 identifier to your GitHub page you need to follow the process that is written in many blogs like in the one OP posted https://nvk.org/n00b-nip5.

But there's a catch that stopped my process for a few hours.

I found out that you need to include a new empty file in the root directory named .nojekyll

What this does is explained here https://github.blog/2009-12-29-bypassing-jekyll-on-github-pages/