DCWL-1486 Added a note to the "Testing" section of the API documentation

for customs-inventory-linking-exports.

public/api/conf/common/testing.md

@@ -0,0 +1,3 @@
+You can use the [HMRC Developer Sandbox](https://developer.service.hmrc.gov.uk/api-documentation/docs/testing) to test the API. The Sandbox is an enhanced testing service that functions as a simulator of HMRC’s production environment.
+
+**Note:** The Customs Inventory Linking Exports API is [user restricted](https://developer.service.hmrc.gov.uk/api-documentation/docs/authorisation/user-restricted-endpoints). For some message types, the person who grants authority to the software must be authorised for that functionality.  This means that you must generate an authorised test user if you want to test all the functionality. Use the [Create Test User API](https://developer.service.hmrc.gov.uk/api-documentation/docs/api/service/api-platform-test-user/1.0) to generate the test user, passing an appropriate EORI from the CDS Test Data Library. You can download the CDS Test Data Library from the [CDS Technical Documentation](https://developer.service.hmrc.gov.uk/guides/customs-declarations-end-to-end-service-guide/#technical-documentation).