npm has two ways of installing modules - either as a local module or a global module.
When installed as a global module (by using the -g option) then it will place any scripts the module provides onto your path so they can be run from anywhere.
When installed as a local module (as you are doing here) then it does not put the scripts onto your path.
To run node-red when it has been installed into a local directory you would run:
node node_modules/node-red/red.js
You may also want to look at New Utility: alternate-node-red-installer
