Add README for enforcing CI maintenance window rules

This README provides details on enforcing CI maintenance windows for change requests, including configuration options and references to relevant APIs.

Author: hanna-g-sn

Server-Side Components/Business Rules/Enforce CI maintenance window on Change schedule/README.md

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+# Enforce CI maintenance window on Change schedule
+
+## What this solves
+Change requests are sometimes scheduled outside the maintenance windows of the affected CIs, causing risky or blocked implementations. This rule validates the planned start and end times of a Change against the maintenance schedules of its related CIs and blocks the update if none of the CIs allow that window.
+
+## Where to use
+- Table: `change_request`
+- When: before insert and before update
+- Order: early (for example 50)
+
+## How it works
+- Looks up CIs related to the Change via `task_ci`
+- For each CI with a defined `maintenance_schedule` (reference to `cmn_schedule`), uses `GlideSchedule.isInSchedule` to verify the planned start and end are inside the window
+- If at least one CI’s maintenance schedule permits the window, the Change is allowed
+- If no related CI permits the window, the rule aborts the action with a clear message
+- Behaviour for CIs without a defined maintenance schedule is configurable
+
+## Configure
+At the top of the script:
+- `BLOCK_WHEN_NO_SCHEDULE`: if true, treat CIs without a maintenance schedule as non-compliant
+- `REQUIRE_BOTH_BOUNDARIES`: if true, both planned start and planned end must be inside a permitted window
+- `TIMEZONE`: optional IANA time zone string (for example `Europe/London`); leave blank to use the schedule or instance default
+
+## Notes
+- If your process requires all CIs to permit the window, change `anyPass` logic to `allPass`
+- This rule checks only maintenance windows defined on the CI record. If you store schedules at the Business Service level, adapt the CI lookup accordingly
+
+## References
+- GlideSchedule API  
+  https://www.servicenow.com/docs/bundle/zurich-api-reference/page/app-store/dev_portal/API_reference/GlideSchedule/concept/c_GlideScheduleAPI.html
+- GlideDateTime API  
+  https://www.servicenow.com/docs/bundle/zurich-api-reference/page/app-store/dev_portal/API_reference/GlideDateTime/concept/c_GlideDateTimeAPI.html
+- Change Management fields  
+  https://www.servicenow.com/docs/bundle/zurich-it-service-management/page/product/change-management/concept/change-management-overview.html
+- Task CI relationship (`task_ci`)  
+  https://www.servicenow.com/docs/bundle/zurich-servicenow-platform/page/product/configuration-management/reference/task-ci.html