Added link to zmq installation instructions

Otherwise error may occur during build time:

  CXX(target) Release/obj.target/binding/binding.o
../binding.cc:28:10: fatal error: 'zmq.h' file not found
         ^
1 error generated.
make: *** [Release/obj.target/binding/binding.o] Error 1
Merge pull request #159 from bobrik/patch-1

Added link to zmq installation instructions