feat(login) adds managed identity login to readme

Author: Undermyspell

docs/features/08-azure-login.md

@@ -5,12 +5,26 @@ developer and technical accounts should always be supported to run the IaC appli
 perspective, to prevent technical account identifiers and secrets to be passed around by developers. 
 
 In the default setup, calling Login() will log the user in (if not already logged in) via normal prompts via azure CLI. 
-If viper variables for service principal info are set (check the code docs on `azure_login.New` or `NewWithParams` methods), 
-then the service principal login will be used (useful for CI systems).
+If specific viper variables are set (check the code docs on `azure_login.New` or `NewWithParams` methods), the following login methods are also supported (useful for CI systems).
 
-# usage
+## Managed identity
+You can provide a flag whether to use azure managed identities for the login. 
+### User assigned managed identity
+Login via a user assigned managed identity can be done by additionally providing the client id.
+### System assigned managed identity
+The system assigned managed identity is used when the client id is ommitted
+
+## Service Principal
+By providing the client-id, client-secret, tenant-id you can login via a service principal as well. You also have to ommit the flag to use a managed identity.
+
+## Usage
 
 ```go
 login := azure_login.New(hq.GetExecutor())
 login.Login()
-```
+```
+The login mechanisms which will be attempted in the following order:
+- User assigned managed identity
+- System assigned managed identity
+- Service Principal
+- Normal user login