Update docs/configuring-playbook-client-schildichat: add a simple explanation

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

docs/configuring-playbook-client-schildichat.md

@@ -1,6 +1,7 @@
 # Configuring SchildiChat (optional)
 
 This playbook can install the [SchildiChat](https://github.com/SchildiChat/schildichat-desktop) Matrix web client for you.
+SchildiChat is a feature-rich messenger for Matrix based on Element with some extras and tweaks.
 SchildiChat can be installed alongside or instead of Element.
 
 **WARNING**: SchildiChat Web is based on Element-web, but its releases are lagging behind. As an example (from 2024-02-26), SchildiChat Web is 22 releases behind (it being based on element-web `v1.11.36`, while element-web is now on `v1.11.58`). Element-web frequently suffers from security issues, so running something based on an ancient Element-web release is **dangerous**. Use SchildiChat Web at your own risk!