[Eng] Add comment for label Legacy (#27134)

* Add comment for label Legacy

* fix indentation

Author: VeryEarly

.github/workflows/script/PrLabeled.ps1

@@ -28,6 +28,14 @@ Please resolve all open review comments and make sure all CI checks are green. R
 "@
     "codegen-survey" = @"
 Thanks for using autorest.powershell to develop your PowerShell module! Would you like to take [a 5-minute survey](https://forms.office.com/r/j6rQuFUqUf?origin=lprLink) to help us improve the tool? Much appreciated :)
+"@
+    "Legacy" = @" 
+To improve dev experience and reduce maintenance efforts, we are deprecating branch: generation now. Azure-PowerShell modules generated by autorest.powershell no longer target branch generation, and will be targeting directly to main instead.
+
+Please find migration guide and document below:
+- [If you have open PR or on going development](https://gist.github.com/VeryEarly/0c748e7bb8f18d9a87228956dc797bc5)
+- [If you are about to start new development and have prior experience](https://gist.github.com/VeryEarly/53cf3372a1c7c7c6f5e1ffd3949513a5)
+- [Starting from scratch](https://eng.ms/docs/cloud-ai-platform/azure-core/azure-experiences-and-ecosystems/azure-portal-and-client-tools-ruhim/azure-cli-tools-azure-cli-powershell-and-terraform/azure-cli-tools/onboarding/azurepowershell/dev_guidance_codegen)
 "@
 }