Fix dependencies on vanilla install #22
Description
The project has dependencies which require cmake, icu4c and node to be installed. The rubygem should either gracefully fail with meaningful messages if they aren't installed, or should offer to install them if the machine it is running on is well understood.
Ruby code like: system('command -v node &> /dev/null') and /darwin/ =~ RUBY_PLATFORM or Gem::Platform.local.os should help.