CB-5248 Fix cordova create directory_name com.example.app AppName extra_arg

Follow up to CB-4748
* Treat string as fourth argument to `cordova create` as JSON
* Properly document arguments to `cordova create` in `cordova help`
CB-5311 windows: Provide cmd script so top level node commands run smoothly
CB-5325 Improve README
CB-5343 Tell people to run npm install when requirements are missing