generate go sdk for authorization (Azure#11942)

Author: njuCZ

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

@@ -18,6 +18,7 @@ batch:
   - tag: package-2018-01-01-preview
   - tag: package-2018-07-01-preview
   - tag: package-2018-09-01-preview
+  - tag: package-2020-04-preview
 ```
 
 ### Tag: package-2015-07-01 and go
@@ -64,3 +65,12 @@ Please also specify `--go-sdk-folder=<path to the root directory of your azure-s
 ``` yaml $(tag) == 'package-2018-09-01-preview' && $(go)
 output-folder: $(go-sdk-folder)/services/preview/$(namespace)/mgmt/2018-09-01-preview/$(namespace)
 ```
+
+### Tag: package-2020-04-preview and go
+
+These settings apply only when `--tag=package-2020-04-preview --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-2020-04-preview' && $(go)
+output-folder: $(go-sdk-folder)/services/preview/$(namespace)/mgmt/2020-04-01-preview/$(namespace)
+```