Added documentation, clarification of purpose in README.md

Added an english version of basic high level documentation, added content to the readme file. Please review the english PDF for accuracy as I do not know estonian and cannot reliably validate any of the translation. PDF dug up by http://www.reddit.com/r/netsec/comments/1i6ajr/estonias_evoting_source_code_made_public/cb5gfbs.