README.md updated

- Path added to run meteor in the correct directory
UI updates and file cleanups

- Bootstrap updated to v3.1.1- Minified Bootstrap added and referenced
for faster loading
- Reference to Modernizr removed (it wasn’t being loaded)
- Added scrolling after URL is shortened so mobile users can see the
shortened URL beneath the fold
- checkPrefixForURLField moved to change event listener on the input
field
- required and type=url added to input field
- CSS cleaned up
- UI updates