Update README.md

Removing reference to Postman

Author: MashaMSFT

README.md

@@ -141,7 +141,7 @@ dotnet run
 Now listening on: https://localhost:5001
 ```
 
-Using a REST Client (like [Insomnia](https://insomnia.rest/), [Postman](https://www.getpostman.com/) or curl), you can now call your API, for example:
+Using a REST Client (such as [Visual Studio](https://learn.microsoft.com/aspnet/core/test/http-files), [Insomnia](https://insomnia.rest/), [Curl](https://curl.se/docs/httpscripting.html) or PowerShell's [Invoke-RestMethod](https://learn.microsoft.com/powershell/module/microsoft.powershell.utility/invoke-restmethod))), you can now call your API, for example:
 
 ```bash
 curl -s -k -H "fromVersion: 0" --url https://localhost:5001/trainingsession/sync