Add deprecation warnings

Signed-off-by: Olivier Wilkinson (reivilibre) <olivier@librepush.net>

CHANGES.md

 Synapse 1.18.0 (2020-07-30)
 ===========================
 
+Deprecation Warnings
+--------------------
+
+### Docker Tags with `-py3` Suffix
+
+Docker `-py3` suffix will be removed in future versions
+
+From 10th August 2020, we will no longer publish Docker images with the `-py3` tag suffix. The images tagged with the `-py3` suffix have been identical to the non-suffixed tags since release 0.99.0, and the suffix is obsolete.
+
+On 10th August, we will remove the `latest-py3` tag. Existing per-release tags (such as `v1.18.0-py3`) will not be removed, but no new `-py3` tags will be added.
+
+Scripts relying on the `-py3` suffix will need to be updated.
+
+
+### TCP-based Replication
+
+When setting up worker processes, we now recommend the use of a Redis server for replication. The old direct TCP connection method is deprecated and will be removed in a future release. See [docs/workers.md](https://github.com/matrix-org/synapse/blob/release-v1.18.0/docs/workers.md) for more details.
+
+
 Improved Documentation
 ----------------------
 

UPGRADE.rst

@@ -75,6 +75,23 @@ for example:
      wget https://packages.matrix.org/debian/pool/main/m/matrix-synapse-py3/matrix-synapse-py3_1.3.0+stretch1_amd64.deb
      dpkg -i matrix-synapse-py3_1.3.0+stretch1_amd64.deb
 
+Upgrading to v1.18.0
+====================
+
+Docker `-py3` suffix will be removed in future versions
+
+From 10th August 2020, we will no longer publish Docker images with the `-py3` tag suffix. The images tagged with the `-py3` suffix have been identical to the non-suffixed tags since release 0.99.0, and the suffix is obsolete.
+
+On 10th August, we will remove the `latest-py3` tag. Existing per-release tags (such as `v1.18.0-py3`) will not be removed, but no new `-py3` tags will be added.
+
+Scripts relying on the `-py3` suffix will need to be updated.
+
+Redis replication is now recommended in lieu of TCP replication
+---------------------------------------------------------------
+
+When setting up worker processes, we now recommend the use of a Redis server for replication. **The old direct TCP connection method is deprecated and will be removed in a future release.**
+See `docs/workers.md <docs/workers.md>`_ for more details.
+
 Upgrading to v1.14.0
 ====================