Add a Read the Docs integration
Short actionable issue extracted from #227 (closed)
Upstream GitLab doesn't need such an integration because Read the Docs has a GitLab integration. It would be better not to propose the new integration on Git projects for clarity (only one way of doing things) if possible
The payload to send is quite simple: https://docs.readthedocs.io/en/stable/webhooks.html#using-the-generic-api-integration