docs(gatsby-plugin-react-helmet): add React hooks compatibility information (#12873)
docs(gatsby-plugin-react-helmet): add React hooks compatibility information (#12873)

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## Description

In the linked issue, it was brought up that documentation should be introduced to alert users of `gatsby-plugin-react-helmet` of the issues Hooks bring, and how to resolve them. This PR is a transcription of the outcomes of that discussion into the documentation, resolving #12357.
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## Related Issues
#12357
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  Link to the issue that is fixed by this PR (if there is one)
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ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,ChristopherBiscardi/gatsby