Please follow the instructions exactly

- the file need to be named 'package.json' - no other name will work!
And you don't need a 'json' editor, any text editor will do!
For more information about the package.json' file from NW.js please see also here:
http://docs.nwjs.io/en/latest/References/Manifest%20Format/
In that file settings like the window size, the icon and so could be added.