Output a .json file with the permalink key

In our front matter we set the permalink key to a value that ends with a .json extension.

---
permalink: "./searchable-data.json"
---

So, a file named searchable-data.njk will be output as a .json file in our output directory.

root-directory
|-- _site
|   |-- searchable-data.json
|   `-- index.html
|-- searchable-data.njk
`-- index.html

... Cool, now we know.