message: Update Go readme
diff: @@ -23,6 +23,16 @@ azure-arm: true
  batch:
  - tag: package-2020-01
  - tag: package-2019-01-preview
  + - tag: package-preview-2021-09
  +```
  +
  +### Tag: package-preview-2021-09
  +
  +These settings apply only when `--tag=package-preview-2021-09 --go` is specified on the command line.
  +Please also specify `--go-sdk-folder=<path to the root directory of your azure-sdk-for-go clone>`.
  +
  +```yaml $(tag) == 'package-preview-2021-09' && $(go)
  +output-folder: $(go-sdk-folder)/services/preview/$(namespace)/mgmt/2021-09-01-preview/$(namespace)
  ```
  ### Tag: package-2020-01 and go
  