[docs] fix chat link

[Conduitry]

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Tests

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This adds a rel=external to the Discord chat link, which is necessary now that endpoints are no longer handled by the client-side router. It also adds a "the".

[Conduitry]

I'd forgotten the main place this needs to be fixed is in the site-kit repo. I'm going to go merge that PR and release that project and bump the version here as part of this PR. Marking as draft.