Readme should explain the use of an API endpoint

[tidoust]

Via web-platform-dx/web-features#204 (comment)

The code fetches data from an API endpoint, currently: https://api.webstatus.dev/v1/features/. That fact should be documented in the Readme, along with possible implications from a data privacy perspective, as that may have impacts on web sites that want to integrate a Baseline status widget.

[aral]

Especially given that said site is run by Google, a surveillance capitalist.

https://github.com/GoogleChrome/webstatus.dev/wiki/About-Web-Platform-Status