Add policy for gatsby cloud references in OSS (#21461)
Add policy for gatsby cloud references in OSS (#21461)

* Add policy for gatsby cloud references in OSS

* Update docs/contributing/gatsby-style-guide.md

Co-Authored-By: Aisha Blake <0361fe97c7c02ef86800dedecb1220f5cf5f3320@gatsbyjs.com>

* Update docs/contributing/gatsby-style-guide.md

Co-Authored-By: Aisha Blake <0361fe97c7c02ef86800dedecb1220f5cf5f3320@gatsbyjs.com>

* Update docs/contributing/gatsby-style-guide.md

* Update docs/contributing/gatsby-style-guide.md

* Add periods to ends of sentences

Co-authored-by: Aisha Blake <0361fe97c7c02ef86800dedecb1220f5cf5f3320@gatsbyjs.com>

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