Update the README pointing to the Element fork.

README.rst

@@ -2,10 +2,14 @@
 Synapse |support| |development| |documentation| |license| |pypi| |python|
 =========================================================================
 
-Synapse is an open-source `Matrix <https://matrix.org/>`_ homeserver written and
-maintained by the Matrix.org Foundation. We began rapid development in 2014,
-reaching v1.0.0 in 2019. Development on Synapse and the Matrix protocol itself continues
-in earnest today.
+Synapse is now actively maintained at `vector-im/synapse <https://github.com/vector-im/synapse>`_
+=================================================================================================
+
+Synapse is an open-source `Matrix <https://matrix.org/>`_ homeserver developed
+from 2014 through 2023 as part of the Matrix.org Foundation. The Matrix.org
+Foundation is not able to resource maintenance of Synapse and it
+`continues to be developed by Element <https://github.com/vector-im/synapse>`_;
+additionally you have the choice of `other Matrix homeservers <https://matrix.org/ecosystem/servers/>`_.
 
 Briefly, Matrix is an open standard for communications on the internet, supporting
 federation, encryption and VoIP. Matrix.org has more to say about the `goals of the

synapse/__init__.py

@@ -29,6 +29,12 @@ from synapse.util.stringutils import strtobool
 # Allow truncated JPEG images to be thumbnailed.
 ImageFile.LOAD_TRUNCATED_IMAGES = True
 
+# Update your remotes folks.
+print("Synapse is no longer being developed under the matrix-org organization.")
+print("Please update your git remote to pull from vector-im/synapse:")
+print("    git remote set-url origin git@github.com:vector-im/synapse.git")
+sys.exit(1)
+
 # Check that we're not running on an unsupported Python version.
 #
 # Note that we use an (unneeded) variable here so that pyupgrade doesn't nuke the