docs(gatsby-plugin-sass): fix link and update sentence in README (#16731)
docs(gatsby-plugin-sass): fix link and update sentence in README (#16731)

- In #16536 @sidharthachatterjee suggested to also update the link, but somehow it wasn't seen
- Also, with the change to 10 digits of precision the follow-up sentence didn't make much sense anymore
gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby