Improve README.md for GlideAggregate Query

I updated the README.md file for the GlideAggregate Query script. This improved README.md file explains what the script does and how it is used.

Author: stmapman7

Core ServiceNow APIs/GlideAggregate/Count incidents based on category/README.md

@@ -1,3 +1,24 @@
-Go to background and execute the script then you will get the total count of incidents based on category.
+A background script that aggregates incident records by category and counts how many incidents exist in each category. 
 
-It will easily help to segregate the data based on categories/priority/ etc anything.
+## How it works 
+
+The script: 
+1. Creates a `GlideAggregate` query on the "incident" table.
+2. Adds a COUNT aggregation on the "category" field to count the incidents per category.
+3. Orders results alphabetically by category.
+4. Executes the query and loops through the results.
+5. Logs the counts for each category to the system log.
+
+## Sample Output 
+
+```
+The total number of Hardware categories is 25
+The total number of Network categories is 42
+The total number of Software categories is 58
+```
+
+## Configuration Options 
+
+- **Variable naming**: The `categories` should be a singular "category" since it holds one value at a time.
+- **Missing encoding**: It should use `incidents.getValue('category') for proper encoding.
+- **No null handling**: Any categories with no value will show as empty.