Send approval pending email during registration

lib/pleroma/emails/user_email.ex

@@ -93,6 +93,19 @@ defmodule Pleroma.Emails.UserEmail do
     |> html_body(html_body)
   end
 
+  def approval_pending_email(user) do
+    html_body = """
+    <h3>Awaiting Approval</h3>
+    <p>Your account at #{instance_name()} is being reviewed by staff. You will receive another email once your account is approved.</p>
+    """
+
+    new()
+    |> to(recipient(user))
+    |> from(sender())
+    |> subject("Your account is awaiting approval")
+    |> html_body(html_body)
+  end
+
   @doc """
   Email used in digest email notifications
   Includes Mentions and New Followers data