Edited readme for Localhost section to refer to Ngrok 

Hello Diego81,

This gem has helped me a lot with a project so I wanted to contribute. I noticed that `localtunnel` is no longer active. I found an alternative in ngrok and it has worked successfully for me. I wanted to help by updating your README file. 

Please feel free to be harsh on my grammar. 

Thanks again! And keep up the great work.