Example authenticating with AzureAD (go-gorm#135)

* Use azuread mssql driver

* spacing

Author: brian-pickens

README.md

@@ -13,4 +13,19 @@ dsn := "sqlserver://gorm:LoremIpsum86@localhost:9930?database=gorm"
 db, err := gorm.Open(sqlserver.Open(dsn), &gorm.Config{})
 ```
 
+## Azure AD Auth
+
+```go
+import (
+  "github.com/microsoft/go-mssqldb/azuread"
+  "gorm.io/driver/sqlserver"
+  "gorm.io/gorm"
+)
+
+// github.com/microsoft/go-mssqldb
+dsn := "sqlserver://gorm:LoremIpsum86@localhost:9930?database=gorm"
+dialector := &sqlserver.Dialector{Config: &sqlserver.Config{DSN: dsn, DriverName: azuread.DriverName}}
+db, err := gorm.Open(dialector, &gorm.Config{})
+```
+
 Checkout [https://gorm.io](https://gorm.io) for details.