Some Changes at README.md

Guys, I changed command to start the server and its URL on README File.
I changed the command because the jekyll raises a deprecation warning.

I also changed the URL to access the server too.

![screen shot 2013-08-13 at 10 31 20 am](https://f.cloud.github.com/assets/410080/954719/c23fba34-041c-11e3-9c4c-e640217f8d91.png)