[#30] Update README file

This change resolves #30 - adds new information to README file, performs some formatting for better readability and updates DEPENDENCIES section due to #33.

Verification:  
* Read entire README file, check for spelling errors, verify if all that is written makes sense and will be a good introductory file for others.  
* Check new [wiki page](https://github.com/nfprojects/nfengine/wiki/Introduction), which is a Markdown-formatted version of README file.