How do I add an index page to the GitLab bundled NGINX?

I've recently installed GitLab, and I'm using the bundled NGINX with it. I've been able to successfully set it up, and put it on mydomain.com/lab

Great! Only problem is that when you go to mydomain.com, it has a 404 page. Well, duh. I need to upload my index.html... but WHERE do I do it? How can I add my index page to the bundled NGINX? Most of all, WHERE do I upload it?

I'm using CentOS 7, and for the love of God I swear I've looked in every directory and I have no idea where to throw my index page in. Please bear with my ignorance as I'm quite new to this.

Thanks, Joel.