How to use theine when not using Gemfile

The README given just instruction how to use theine when gem is in Bundler (but installation suggest using RubyGems). 
'bundle exec theine_server' will end up with:
'Gem::LoadError: theine is not part of the bundle. Add it to Gemfile.'
Merge pull request #1 from BartlomiejSkwira/patch-1

How to use theine when not using Gemfile