track1 add batch tag synapse (#15799)

Author: Alancere

specification/synapse/resource-manager/readme.go.md

@@ -16,6 +16,7 @@ batch:
   - tag: package-2019-06-01-preview
   - tag: package-2020-12-01
   - tag: package-2021-03
+  - tag: package-preview-2021-06
 ```
 
 ### Tag: package-2019-06-01-preview and go
@@ -43,4 +44,13 @@ Please also specify `--go-sdk-folder=<path to the root directory of your azure-s
 
 ``` yaml $(tag) == 'package-2021-03' && $(go)
 output-folder: $(go-sdk-folder)/services/$(namespace)/mgmt/2021-03-01/$(namespace)
+```
+
+### Tag: package-preview-2021-06 and go
+
+These settings apply only when `--tag=package-preview-2021-06 --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-2021-06' && $(go)
+output-folder: $(go-sdk-folder)/services/preview/$(namespace)/mgmt/2021-06-01-preview/$(namespace)
 ```