Add package.json for npm

[cooperka]

This is awesome! I saw it was a few years old but with plenty of stars, so I figured it would be worth hosting on npm for others to find and use more easily.

To publish publicly (after installing npm) you can just run npm publish.

The install step that I added to the README will link the git-fem binary automatically, so no need to clone or make install in order to use it. See docs here.

I think license is required, so I defaulted to MIT which seems to be the de-facto standard for open source hobby projects. Feel free to tweak it before merging.

[cooperka]

Hi @ashaindlin, not sure if you're monitoring this repo but I'd love to hear your thoughts on this.