Add README.md

Instructions about the overview of the script

Author: nvprav

Server-Side Components/Background Scripts/User Email mismatch with Cmn Notif device/README.md

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+# Email Mismatch Checker
+
+## Description
+
+This ServiceNow background script checks for mismatches between notification devices and user records based on email addresses.
+
+It looks for active `cmn_notif_device` records that:
+- Have a non-null `email_address`
+- Are linked to a user
+- Are of type "Email"
+- Are named "Primary Email"
+
+Then it verifies if a matching user exists in the `sys_user` table with the same email. If no match is found, the mismatch is logged.
+
+## How to Use
+
+1. Go to **Scripts > Background** in your ServiceNow instance.
+2. Paste the script.
+3. Run the script.
+4. Check the system logs for mismatch details.
+
+## Output
+
+Logs the number of mismatches and details like:
+Mismatch: Device=<device_name>, Device Email=<email_address>