[Stk] Readme files update

[Ariel Elkin]

Hey all,

I’m currently making a Cocoapod for the STK. One of the requirements is for the library to have a LICENSE file. 

So I thought I’d place the License text in the current README into its own file. The text could also be duplicated in the README, but I think it makes more sense for it to be in its own file.

I’ve also polished the README file a little bit so that it’s easier to read on GitHub. In the first section, I made the bulleted list link to different section headers so that it acts a better table of contents. 

Cheers

Ariel