Remove Link About Polyfill Strategy due to Link to Polyfill.io

[34638a]

Hi BC Team,

In an effort to make the internet a safer place for Bigcommerce end users (innocent shoppers), I would like to request a update to the ReadMe on cornerstone to either include a disclaimer about, or updated article link regarding the note on Polyfill strategy due to the Polyfill.io incident. The article, that is currently linked, endorses Polyfill.io under section User agent parsing.

This request is made in an effort to minimise its visibility, to avoid potentially having polyfill.io be linked on a ecommerce website, post supply chain attack incident.

Citations related to the supply chain attack: Kaspersky Cloudflare