You can post your site on the Internet for free with GitHub Pages. The URL will have 'github.io' in it, but you will be able to show it as a prototype to your clients and colleagues.
On GitHub, navigate to your site's repository.
Under your repository name, click Settings.
In the left sidebar, click Pages.
Under "GitHub Pages", use the None or Branch drop-down menu and select a publishing source.
Optionally, use the drop-down menu to select a folder for your publishing source.
Click Save.
Identify the folder path in your Github repository, and the name of the file you're trying to load in the browser URL:
Those will correspond to the browser URL for page published on Github.io: