readme: how to set the privacy policy url

Author: Johnson145

Auth/README.md

@@ -213,7 +213,7 @@ Auth.defaultAuthUI.handleOpenURL(url, sourceApplication: sourceApplication)
 We support cross device email link sign in for the normal flows. It is not supported with anonymous user upgrade. By default, cross device support is enabled. You can disable it setting `forceSameDevice` to false in the `FUIEmailAuth` initializer.
 
 ## Customizing FirebaseUI for authentication
-### Custom terms of Service (ToS) URL
+### Custom Terms of Service (ToS) and privacy policy URLs
 
 The Terms of Service URL for your application, which is displayed on the
 email/password account creation screen, can be specified as follows:
@@ -229,6 +229,13 @@ authUI?.tosurl = kFirebaseTermsOfService
 authUI.TOSURL = [NSURL URLWithString:@"https://example.com/tos"];
 ```
 
+The same applies to the URL of your privacy policy:
+```swift
+// Swift
+let kFirebasePrivacyPolicy = URL(string: "https://policies.google.com/privacy")!
+authUI?.privacyPolicyURL = kFirebasePrivacyPolicy
+```
+
 ### Custom strings
 
 You can override the default messages and prompts shown to your users. This can