Add typescript types

[QAComet]

I added a basic typescript interface so I could run this package in one of my projects. Now in typescript I can use

import whyIsNodeRunning from 'why-is-node-running';

async function errorFunc () : void {
  // ...
  whyIsNodeRunning();
}

[jonkoops]

Hi @QAComet, thanks for your PR. In the mean time we've changed the package use JavaScript modules, so I don't think the types here are correct any longer as they use a namespace. I'll go ahead an close this PR for now, but I intend to add types going forward.