[mod] add a README

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

README.rst

@@ -0,0 +1,14 @@
+.. SPDX-License-Identifier: AGPL-3.0-or-later
+
+==============================
+Only show green hosted results
+==============================
+
+A `SearXNG plugin <https://docs.searxng.org/dev/plugins.html>`__ to check if a
+domain is part of the `Green WEB <https://www.thegreenwebfoundation.org/>`__.
+
+Its recommended to install (and regularly update) `The Green Domains dataset
+<https://github.com/thegreenwebfoundation/admin-portal/blob/master/docs/working-with-greenweb-datasets.md>`__
+otherwise the plugin uses the API what sends a lot of requests from the SearXNG
+instance to the Green WEB foundation and slows down the SearXNG instance
+massively.