Update website to indicate community chat has moved from Slack to Discord (#3545)
Update website to indicate community chat has moved from Slack to Discord (#3545)

Summary:
My understanding is the the Slack server is moving to Discord, and I think it makes sense to move with them.

![Screen Shot 2021-07-15 at 2 19 11 PM](https://user-images.githubusercontent.com/162735/125859374-471f6cfc-93cb-4c9e-b6fe-6c8611d59b4a.png)

Pull Request resolved: https://github.com/facebook/relay/pull/3545

Test Plan:
{F632331716}
Imported from GitHub, without a `Test Plan:` line.

|[Site Preview: relay](https://our.intern.facebook.com/intern/staticdocs/eph/D29721043/V4/relay/)

Reviewed By: poteto

Differential Revision: D29721043

Pulled By: captbaritone

fbshipit-source-id: 09586feefaf045a81dee7faaefad7cd473a167c7

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