Update README

* add information about the customizations provided in this module

README.rst

 ..
-    Copyright (C) 2020 - 2021 TU Wien.
+    Copyright (C) 2020-2022 TU Wien.
 
     Invenio-Config-TUW is free software; you can redistribute it and/or
     modify it under the terms of the MIT License; see LICENSE file for more
@@ -9,5 +9,55 @@
  Invenio-Config-TUW
 ====================
 
-Invenio module containing some customizations and configuration for TU Wien.
+Invenio module for tweaking InvenioRDM to the needs of TU Wien.
 
+We use this module to customize the following:
+
+* Permission policies
+* OIDC authentication handling
+* E-Mail notification on errors
+* Configuration values
+
+
+Details
+=======
+
+Permission policies
+-------------------
+
+Currently, we are still operating on a friendly-user basis.
+That is, while we cannot lose any data that has been uploaded by our users, we do not
+allow every registered user to create record drafts, upload data, or publish records
+from the get-go.
+Instead, we require users to have the ``trusted-user`` role in order to be able to
+create record drafts and upload data.
+Similarly, we have the ``trusted-publisher`` role as a requirement for publishing
+records.
+Generally, these roles have to be assigned to users manually by an administrator.
+
+On the test system, we give out these permissions automatically if we detect that a
+newly registered user is an employee of TU Wien.
+
+
+OIDC authentication handling
+----------------------------
+
+Because we have some special requirements regarding the authentication and signup
+process, we have customized some of the handler functions for the OAuth client
+that's integrated in InvenioRDM.
+These customizations are contained in the files in ``auth/``.
+
+
+E-Mail notification on errors
+-----------------------------
+
+This module defines a custom log handler for error-level logs which sends out
+notifications as e-mail to a set of configured recipient addresses.
+
+
+Configuration values
+--------------------
+
+Last but not least, we also set some default configuration values for deployments
+of InvenioRDM at TU Wien.
+The relevant files here are ``config.py`` and ``ext.py``.