Fix action.yml template expression error

- Removed template expression example from changeset_variables input description
- Template expressions are not allowed in input descriptions (only in output values)
- Refer users to README for usage examples

Author: oden3000

action.yml

@@ -36,7 +36,7 @@ inputs:
     required: false
     default: 'false'
   changeset_variables:
-    description: 'Changeset variables in KEY=VALUE format (one per line). Allows injecting secrets from GitHub Secrets without storing in version control. Example: DB_PASSWORD=${{ secrets.DB_PASSWORD }}'
+    description: 'Changeset variables in KEY=VALUE format (one per line). Allows injecting secrets from GitHub Secrets without storing in version control. See README for examples.'
     required: false
 
 outputs: