feat(ruby): Add cron upsert docs (#8319)

src/platform-includes/crons/setup/ruby.mdx

@@ -71,3 +71,50 @@ If your job execution fails, you can notify Sentry about the failure:
 ```ruby
 Sentry.capture_check_in('<monitor-slug>', :error)
 ```
+
+## Upserting Cron Monitors
+
+You can create and update your Monitors programmatically with code
+rather than [creating and configuring them in Sentry.io](https://sentry.io/crons/create/).
+
+First create a config object from either a crontab or an interval.
+
+```ruby
+# Create a config from a crontab schedule (every 10 minutes)
+monitor_config = Sentry::Cron::MonitorConfig.from_crontab(
+  '5 * * * *',
+  checkin_margin: 5, # Optional check-in margin in minutes
+  max_runtime: 15, # Optional max runtime in minutes
+  timezone: 'Europe/Vienna', # Optional timezone
+)
+
+# Create a config from an interval schedule (every 10 minutes)
+monitor_config = Sentry::Cron::MonitorConfig.from_interval(
+  10,
+  :minute,
+  checkin_margin: 5, # Optional check-in margin in minutes
+  max_runtime: 15, # Optional max runtime in minutes
+  timezone: 'Europe/Vienna', # Optional timezone
+)
+```
+
+Then, use that config object during your check-ins.
+
+```ruby
+# 🟡 Notify Sentry your job is running:
+check_in_id = Sentry.capture_check_in(
+  '<monitor-slug>',
+  :in_progress,
+  monitor_config: monitor_config
+)
+
+# Execute your scheduled task here...
+
+# 🟢 Notify Sentry your job has completed successfully:
+Sentry.capture_check_in(
+  '<monitor-slug>',
+  :ok,
+  check_in_id: check_in_id,
+  monitor_config: monitor_config
+)`
+```