Document how to install/test locally

[tacman]

I've cloned the repo and it run locally as expected. But when I go offline, it doesn't work. I didn't report this as a bug because obviously it does work, so I must be doing something wrong.

git clone [email protected]:wes-goulet/background-noise 
cd background-noise 
php -S localhost:8085 -t .

http://localhost:8085/ works as expected

Now switch throttling to Offline, going to that same url shows a 404.

I don't know if it's because I'm using localhost, or what, but I was wondering if you could clarify how to test offline.