Generate go sdk for keyvault - package-preview-2020-04 (#11187)

Author: njuCZ

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

@@ -13,11 +13,20 @@ go:
 
 ``` yaml $(go) && $(multiapi)
 batch:
+  - tag: package-preview-2020-04
   - tag: package-2019-09
   - tag: package-2018-02
   - tag: package-2016-10
   - tag: package-2015-06
 ```
+### Tag: package-preview-2020-04 and go
+
+These settings apply only when `--tag=package-preview-2020-04 --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-2020-04' && $(go)
+output-folder: $(go-sdk-folder)/services/preview/$(namespace)/mgmt/2020-04-01-preview/$(namespace)
+```
 
 ### Tag: package-2019-09 and go