update autorest command used in README.md (#23039)

Author: YanaXu

src/TrafficManager/TrafficManager.Management.Sdk/README.md

@@ -5,8 +5,7 @@ This directory contains management plane service clients of Az.Storage module.
 In this directory, run AutoRest:
 ```
 autorest --reset
-autorest --use:@microsoft.azure/[email protected]
-autorest.cmd README.md --version=v2
+autorest --use:@autorest/[email protected]
 ```
 
 ### AutoRest Configuration