Add DNS section to wsproxy docs

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2261

docs/configuring-playbook-bridge-mautrix-wsproxy.md

@@ -4,10 +4,20 @@ The playbook can install and configure [mautrix-wsproxy](https://github.com/maut
 
 See the project's [documentation](https://github.com/mautrix/wsproxy#readme) to learn what it does and why it might be useful to you.
 
+
+## DNS
+
+You need to create a `wsproxy.DOMAIN` DNS record pointing to your Matrix server (a `CNAME` pointing to `matrix.DOMAIN`) to use wsproxy.
+The hostname is configurable via a `matrix_mautrix_wsproxy_hostname` variable.
+
+
+## Configuration
+
 Use the following playbook configuration:
 
 ```yaml
 matrix_mautrix_wsproxy_enabled: true
+
 matrix_mautrix_androidsms_appservice_token: 'secret token from bridge'
 matrix_mautrix_androidsms_homeserver_token: 'secret token from bridge'
 matrix_mautrix_imessage_appservice_token: 'secret token from bridge'
@@ -17,6 +27,7 @@ matrix_mautrix_wsproxy_syncproxy_shared_secret: 'secret token from bridge'
 
 Note that the tokens must match what is compiled into the [mautrix-imessage](https://github.com/mautrix/imessage) bridge running on your Mac or Android device.
 
+
 ## Usage
 
 Follow the [matrix-imessage documenation](https://docs.mau.fi/bridges/go/imessage/index.html) for running `android-sms` and/or `matrix-imessage` on your device(s).