Documentation

- added v. basic README.md
- converted BUILD.txt to markdown to be more github friendly
- added some missing stuff in the BUILD instructions

Also, the [link](https://drive.google.com/?tab=mo&authuser=0#folders/0BxZiP9lENIZjZlE1VmNhZGxHc2s/) on the [ispaces webpage](http://www.interactive-spaces.org/home/releases) drops me to my google drive root.