Update Slack link (#963)

Author: Kludex

docs/help.md

@@ -12,6 +12,6 @@ If you're on a [Logfire][logfire] Pro plan, you can also get a dedicated private
 
 The [PydanticAI GitHub Issues][github-issues] are a great place to ask questions and give us feedback.
 
-[slack]: https://join.slack.com/t/pydanticlogfire/shared_invite/zt-2war8jrjq-w_nWG6ZX7Zm~gnzY7cXSog
+[slack]: https://logfire.pydantic.dev/docs/join-slack/
 [github-issues]: https://github.com/pydantic/pydantic-ai/issues
 [logfire]: https://pydantic.dev/logfire