update readme for contact delete

Author: josler

README.md

@@ -335,7 +335,7 @@ contacts = intercom.contacts.find_all(email: "[email protected]")
 intercom.contacts.convert(contact, user)
 
 # Delete a contact
-intercom.contacts.find(id: "some_id").delete
+intercom.contacts.delete(contact)
 ```
 
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