Add README for querying old records with GlideRecord

This README provides a guide on querying records older than a specified number of days using GlideRecord in ServiceNow. It includes details on the solution, usage context, implementation steps, and references to relevant APIs.

Author: hanna-g-sn

Core ServiceNow APIs/GlideRecord/Get Records Older than X Days/README.md

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+# Query records older than N days efficiently
+
+## What this solves
+You often need to find records older than a threshold without loading the world into memory. This snippet:
+- Uses GlideDateTime maths to compute a date boundary
+- Uses encoded queries with index-friendly operators
+- Streams results and logs a compact summary
+
+## Where to use
+Background Script, Script Include utility, or any server-side context.
+
+## How it works
+- Compute a past date with GlideDateTime and subtract days
+- Build an encoded query like `opened_at<javascript:gs.daysAgoStart(n)` or a literal date
+- Limit fields with `addQuery` and `setLimit` when sampling
+
+## References
+- GlideRecord API  
+  https://www.servicenow.com/docs/bundle/zurich-api-reference/page/app-store/dev_portal/API_reference/GlideRecord/concept/c_GlideRecordAPI.html
+- GlideDateTime API  
+  https://www.servicenow.com/docs/bundle/zurich-api-reference/page/app-store/dev_portal/API_reference/GlideDateTime/concept/c_GlideDateTimeAPI.html
+- GlideSystem date helpers  
+  https://www.servicenow.com/docs/bundle/zurich-api-reference/page/app-store/dev_portal/API_reference/GlideSystem/reference/r_GlideSystem-date-methods.html