Add changelog entry for Synapse v0.99

CHANGELOG.md

@@ -1,3 +1,21 @@
+# 2019-02-06
+
+## Synapse v0.99 support and preparation for Synapse v1.0
+
+Matrix is undergoing a lot of changes as it matures towards Synapse v1.0.
+The first step is the Synapse v0.99 transitional release, which this playbook now supports.
+
+If you've been using this playbook successfully until now, you'd be aware that we've been doing [Server Delegation](docs/howto-server-delegation.md) using a `_matrix._tcp` DNS SRV record (as per [Configuring DNS](docs/configuring-dns.md)).
+
+Due to changes related to certificate file requirements that will affect us at Synapse v1.0, we'll have to stop using a **`_matrix._tcp` DNS SRV record in the future** (when Synapse goes to v1.0 - around 5th of March 2019). We **still need to keep the SRV record for now**, for backward compatibility with older Synapse versions (lower than v0.99).
+
+**What you need to do now** is make use of this transitional Synapse v0.99 release to **prepare your federation settings for the future**. You have 2 choices to prepare yourself for compatibility with the future Synapse v1.0:
+
+- (recommended) set up [Server Delegation via a well-known file](docs/howto-server-delegation.md#server-delegation-via-a-well-known-file), unless you are affected by the [Downsides of well-known-based Server Delegation](docs/howto-server-delegation.md#downsides-of-well-known-based-server-delegation). After some time, when most people have upgraded to Synapse v0.99 and older releases have disappeared, be prepared to drop your `_matrix._tcp` SRV record.
+
+- (more advanced) if the [Downsides of well-known-based Server Delegation](docs/howto-server-delegation.md#downsides-of-well-known-based-server-delegation) are not to your liking, **as an alternative**, you can set up [Server Delegation via a DNS SRV record](docs/howto-server-delegation.md#server-delegation-via-a-dns-serv-record-advanced). In such a case, you get to keep using your existing `_matrix._tcp` DNS SRV record forever and need to NOT set up a `/.well-known/matrix/server` file. Don't forget that you need to do certificate changes though. Follow the guide at [Server Delegation via a DNS SRV record](docs/howto-server-delegation.md#server-delegation-via-a-dns-serv-record-advanced).
+
+
 # 2019-02-01
 
 ## TLS v1.3 support