CCM-13011 Fix Postman Sandbox Collection (#424)

* tests

* readme changes

Author: Namitha-Prabhu

README.md

@@ -34,6 +34,7 @@ This repository documents the Supplier API specification and provides an SDK wit
       - [CI (Automatic)](#ci-automatic)
       - [CD (Manual)](#cd-manual)
   - [Licence](#licence)
+  - [Postman](#postman)
 
 ## API Consumers - Getting Started
 
@@ -138,3 +139,15 @@ Deployments can be made of any [release](https://github.com/NHSDigital/nhs-notif
 Unless stated otherwise, the codebase is released under the MIT License. This covers both the codebase and any sample code in the documentation.
 
 Any HTML or Markdown documentation is [© Crown Copyright](https://www.nationalarchives.gov.uk/information-management/re-using-public-sector-information/uk-government-licensing-framework/crown-copyright/) and available under the terms of the [Open Government Licence v3.0](https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/).
+
+## Postman
+
+Included in this repo are postman collections that allows the user to interact with the sandbox APIs.
+
+To use the collections:
+
+Download the json files located in the postman directory
+Import the files into postman
+Select a target environment in postman
+Run the collection
+The collections must be kept in sync manually