Update docs/configuring-playbook-bridge-matrix-bridge-sms.md: create a section for the prerequisite

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

docs/configuring-playbook-bridge-matrix-bridge-sms.md

@@ -4,7 +4,9 @@ The playbook can install and configure [matrix-sms-bridge](https://github.com/be
 
 See the project's [documentation](https://github.com/benkuly/matrix-sms-bridge/blob/master/README.md) to learn what it does and why it might be useful to you.
 
-**The bridge uses [android-sms-gateway-server](https://github.com/RebekkaMa/android-sms-gateway-server). You need to configure it first.**
+## Prerequisite
+
+The bridge uses [android-sms-gateway-server](https://github.com/RebekkaMa/android-sms-gateway-server). You need to configure it first.
 
 ## Adjusting the playbook configuration