docs(auth): windows platform does not support multi-factor auth (#16974)

Author: russellwheatley

docs/auth/multi-factor.md

@@ -16,8 +16,8 @@ more difficult.
 
 ## Before you begin
 
-Note: Using multi-factor authentication with
-[multiple tenants](https://cloud.google.com/identity-platform/docs/multi-tenancy)
+Note: Windows platform does not support multi-factor authentication. Using multi-factor authentication with
+[multiple tenants](https://cloud.google.com/identity-platform/docs/multi-tenancy) on any platform
 is not supported on Flutter.
 
 1.  Enable at least one provider that supports multi-factor authentication.
@@ -108,7 +108,7 @@ To enroll a new secondary factor for a user:
       // ...
     },
     codeAutoRetrievalTimeout: (_) {},
-  ); 
+  );
   ```
 
 1. Once the SMS code is sent, ask the user to verify the code:
@@ -141,7 +141,7 @@ The code below shows a complete example of enrolling a second factor:
     verificationCompleted: (_) {},
     verificationFailed: (_) {},
     codeSent: (String verificationId, int? resendToken) async {
-      // See `firebase_auth` example app for a method of retrieving user's sms code: 
+      // See `firebase_auth` example app for a method of retrieving user's sms code:
       // https://github.com/firebase/flutterfire/blob/main/packages/firebase_auth/firebase_auth/example/lib/auth.dart#L591
       final smsCode = await getSmsCodeFromUser(context);
 
@@ -271,7 +271,7 @@ try {
     verificationCompleted: (_) {},
     verificationFailed: (_) {},
     codeSent: (String verificationId, int? resendToken) async {
-      // See `firebase_auth` example app for a method of retrieving user's sms code: 
+      // See `firebase_auth` example app for a method of retrieving user's sms code:
       // https://github.com/firebase/flutterfire/blob/main/packages/firebase_auth/firebase_auth/example/lib/auth.dart#L591
       final smsCode = await getSmsCodeFromUser(context);
 
@@ -297,7 +297,7 @@ try {
   );
 } catch (e) {
   ...
-} 
+}
 ```
 
 Congratulations! You successfully signed in a user using multi-factor