Add optional welcome message.

lib/pleroma/user.ex

@@ -261,6 +261,7 @@ defmodule Pleroma.User do
   def register(%Ecto.Changeset{} = changeset) do
     with {:ok, user} <- Repo.insert(changeset),
          {:ok, user} <- autofollow_users(user),
+         {:ok, _} <- Pleroma.User.WelcomeMessage.post_welcome_message_to_user(user),
          {:ok, _} <- try_send_confirmation_email(user) do
       {:ok, user}
     end