Open source changelog

Description

• Add shell block around npm install command to be able to copy to clipboard
• format sass syntax
• remove link to starters using sass: none of the starters now use sass

Documentation

https://www.gatsbyjs.com/docs/how-to/styling/sass/ <!-- Where is this feature or API documented?

• If docs exist:
  • Update any references, if relevant. This includes Guides and Gatsby Internals docs.
• If no docs exist:
  • Create a stub for documentation including bullet points for how to use the feature, code snippets (including from happy path tests), etc.
• Tag @gatsbyjs/documentation for review, pairing, polishing of the documentation -->

Related Issues

No related issues <!-- Link to the issue that is fixed by this PR (if there is one) e.g. Fixes #1234

Link to an issue that is partially addressed by this PR (if there are any) e.g. Addresses #1234

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