Put deprecation warnings undre Pleroma.Config.

lib/pleroma/config/deprecation_warnings.ex

@@ -0,0 +1,20 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Config.DeprecationWarnings do
+  require Logger
+
+  def check_frontend_config_mechanism() do
+    if Pleroma.Config.get(:fe) do
+      Logger.warn("""
+      !!!DEPRECATION WARNING!!!
+      You are using the old configuration mechanism for the frontend. Please check config.md.
+      """)
+    end
+  end
+
+  def warn do
+    check_frontend_config_mechanism()
+  end
+end