Install the dotenv package:
$ npm install dotenv
Create a `.env` file in the root of your project, and add your Webmention.io API key
Don't forget to add it to your
.gitignore file. While we are here, let's add the
_cache/ folder which will be created when we first fetch webmentions:
How I added dotenv support to Netlify is covered in this Stack Overflow answer.