Move license to it's own file. 

Hi, 

The 'Getting Started' didn't say *where* to get the boilerplate code.  This commit adds some text for that, and moves the license to it's own file.  It took me a minute to figure out how MEAN.JS was licensed.  Having the license in it's own file is not necessary, but more github standard.

Thanks and looking forward to working with MEAN.JS