Try to improve Dendrite announcement message

This is an attempt to address this:
dc893485d1 (commitcomment-63097721)

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ## Dendrite support
 
-**Existing (Synapse) installations need to be updated**, see below.
+**TLDR**: We now have optional experimental [Dendrite](https://github.com/matrix-org/dendrite) homeserver support for new installations. **Existing (Synapse) installations need to be updated**, because some internals changed. See [Adapting the configuration for existing Synapse installations](#adapting-the-configuration-for-existing-synapse-installations).
 
 [Jip J. Dekker](https://github.com/Dekker1) did the [initial work](https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/818) of adding [Dendrite](https://github.com/matrix-org/dendrite) support to the playbook back in January 2021. Lots of work (and time) later, Dendrite support is finally ready for testing.
 
@@ -12,6 +12,8 @@ The playbook was previously quite [Synapse](https://github.com/matrix-org/synaps
 
 **Synapse is still the default homeserver implementation** installed by the playbook. A new variable (`matrix_homeserver_implementation`) controls which server implementation is enabled (`synapse` or `dendrite` at the given moment).
 
+### Adapting the configuration for existing Synapse installations
+
 Because the playbook is not so Synapse-centric anymore, a small configuration change is necessary for existing installations to bring them up to date.
 
 The `vars.yml` file for **existing installations will need to be updated**:
@@ -26,6 +28,8 @@ The `vars.yml` file for **existing installations will need to be updated**:
 matrix_homeserver_generic_secret_key: "{{ matrix_synapse_macaroon_secret_key }}"
 ```
 
+### Trying out Dendrite
+
 Finally, **to try out Dendrite**, we recommend that you **use a new server** and the following addition to your `vars.yml` configuration:
 
 ```yaml