Update CI guide for Deploio deployments

[coorasse]

The CI page still described the deployment as running to Heroku and didn't reflect what renuo configure-semaphore does today.

• Describe what renuo configure-semaphore sets up (secret, notifications, deployment targets) and link directly to the templates in renuo-cli
• Explain what to adapt: dropping develop, the Deploio project naming the deploy pipelines rely on, the Postgres version, Node.js setup
• Mention the organization-wide nctl secret and the renuo ci commands used for the deployment
• Replace Heroku with Deploio