Update and rename README.md to README.md

Updated the readme to be more descriptive: described the criteria the script evaluates, and added how to use the script.

Author: WillemZeiler

Client-Side Components/Catalog Client Script/Strong Username Validation Script/README.md

@@ -0,0 +1,10 @@
+## Strong Username Validation Script
+This script validates a username entered in a ServiceNow catalog item form. It prevents form submission if the username does not meet the required format.
+
+### Validation Criteria
+The username must start with a letter (a–z or A–Z).
+It must be at least 6 characters long.
+It can only contain letters and numbers.
+
+## Usage
+Add the script as an onSubmit client script in the catalog item. If the username is invalid, an error message is shown and the form is not submitted.