Add mistakenly removed yml

https://trello.com/c/ryoxvses

config/locales/en/errors.yml

@@ -6,6 +6,12 @@ en:
         - Try again later.
         - If you reached this page after submitting information then it has not been saved. You’ll need to enter it again when the service is available.
       support_message: If you have any questions, please email us at %{email_link}
+    not_found:
+      page_title: Page not found
+      instructions:
+        - If you entered a web address, check it is correct.
+        - If you pasted the web address, check you copied the entire address.
+      support_message: "If the web address is correct or you selected a link or button and you need to speak to someone about this problem, contact the %{service_name} team: %{email_link}"
     unprocessable_entity:
       page_title: Sorry, there’s a problem with the service
       instructions: