Adds an example to check if a user exists.

README.md

@@ -124,7 +124,7 @@ $resubscribe = false;
 craft()->oneCampaignMonitor_subscribers->add($list_id, $email, $name, $customFields, $resubscribe);
 ```
 
-Update a user in a list:
+Update a subscriber in a list:
 
 ```
 $list_id = '123';
@@ -135,6 +135,16 @@ $resubscribe = true;
 craft()->oneCampaignMonitor_subscribers->update($list_id, $email, $name, $customFields, $resubscribe);
 ```
 
+Determine if a subscriber exists in a list:
+
+```
+$list_id = '123';
+$email = 'email@email.com';
+if (craft()->oneCampaignMonitor_subscribers->exists($list_id, $email)) {
+  // subscriber exists
+}
+```
+
 ### Checking if the user has subscribed to a list
 
 You can check in a template if the current user (by session) has already subscribed to a list: