changes typos/language in readme.md

Hey! Awesome project—I corrected a few grammar mistakes and changed some awkward language in the readme file. I also added a screenshot of the demo page so users don’t have to click through to get a first impression of the project. Also referred to project by name (baguetteBox.js) instead of ‘it’ (because branding)

![screen shot 2014-08-05 at 5 05 27 pm](https://cloud.githubusercontent.com/assets/6556190/3820772/e215c574-1cfd-11e4-8e19-57a1fc8ecb6d.png)

![screen shot 2014-08-05 at 5 05 42 pm](https://cloud.githubusercontent.com/assets/6556190/3820773/e2186b26-1cfd-11e4-93ae-026e2cbc49a4.png)