doc/integrations: add unofficial Raycast extension

Created by: bobheadxi

Adds my unofficial Raycast for Sourcegraph extension to the integrations list 😛

• https://www.raycast.com/bobheadxi/sourcegraph
• Source: https://github.com/bobheadxi/raycast-sourcegraph
• Tweet: https://twitter.com/sourcegraph/status/1512130089999376387

Test plan