Update communication guide to match style guidelines (#6491)

* Update communication guide to match style guidelines

Update the Zoom and Slack communication guides to match style guidelines. This also includes a few updates, grammar fixes, and modifications from the community.

Co-authored-by: Aaron Epperson <[email protected]>
Co-authored-by: Bob Killen <[email protected]>

* Fix links in slack-guidelines

Co-authored-by: Aaron Epperson <[email protected]>
Co-authored-by: Bob Killen <[email protected]>

Author: 3 people