[Plop] Missing index file

[Connor Bär]

When generating the files for a new React component with plop, the index.js is not generated. I couldn't decide where to add this.

• Should it be an option in the CLI prompt?
• Or should it be added to the files by default?

WDYT @felixjung? I'm happy to make a PR for this :)

[Felix Jung]

Thanks, I noticed this myself and haven't gotten to fixing it, yet. I would want to make this the default for React components. So, you'd need to add an action to that array that the files are being reduced into. I think I'd run reduce over the files concatenated with the default index file. Make sense?