Copyright + gemspec file

while packaging your em-mongo for debian, we have found that the copyright for you is missing.

also we need the readme in the gem to upload into debian, because of the license term.

since we would like to run your spec tests after building the debian package, we also need this.

If you merge this PR, please also release a new version of the gem to rubygems.org, this makes it easier for the debian people  to package your software