Update the iOS documentation on how to manage the badge

docs/delivery_methods/ios.md

@@ -19,7 +19,7 @@ https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_
 ## Usage
 
 ```ruby
-class CommentNotification
+class CommentNotifier < ApplicationNotifier
   deliver_by :ios do |config|
     config.device_tokens = -> { recipient.notification_tokens.where(platform: :iOS).pluck(:token) }
     config.format = ->(apn) {
@@ -83,13 +83,62 @@ end
 Apple Push Notifications may fail delivery if the user has removed the app from their device. Noticed allows you
 
 ```ruby
-class CommentNotification
+class CommentNotifier < ApplicationNotifier
   deliver_by :ios do |config|
     config.invalid_token = ->(token) { NotificationToken.where(token: token).destroy_all }
   end
 end
 ```
 
+## Updating the iOS app badge
+
+If you're managing the iOS app badge, you can pass it along in the format
+
+```ruby
+class CommentNotifier < ApplicationNotifier
+  deliver_by :ios do |config|
+    config.format = ->(apn) {
+      apn.alert = "Hello world"
+      apn.custom_payload = {url: root_url(host: "example.org")}
+      apn.badge = recipient.notifications.unread.count
+    }
+  end
+end
+```
+
+Another common action is to update the badge after a user reads a notification. This is a great use of the   Noticed::Ephemeral class. Since it's all in-memory, it will perform the job and not touch the databse.
+
+```ruby
+class NativeBadgeNotifier < Noticed::Ephemeral
+  deliver_by :ios do |config|
+    config.format = ->(apn) {
+      apn.alert = ios_alert
+      apn.custom_payload = ios_custom_payload
+      apn.badge = recipient.notifications.unread.count
+    }
+  end
+
+  notification_methods do
+    def ios_custom_payload
+      {}
+    end
+
+    # Setting the alert text to nil will deliver the notification in
+    # the background. This is used to update the app badge on the iOS home screen
+    def ios_alert
+      nil
+    end
+  end
+end
+```
+
+Then you can simply deliver this notifier to update the badge when you mark the notification as read
+
+```ruby
+notification.mark_as_read!
+NativeBadgeNotifier.with(record: notification).deliver(notification.recipient)
+```
+
 ## Delivering to Sandboxes and real devices
 
 If you wish to send notifications to both sandboxed and real devices from the same application, you can configure two iOS delivery methods