STA5-SmartLink-command-guidance.md

 # STA5 SmartLink command guidance
 
 *Agenda*
+- [Purpose](#purpose)
 - [Requirement](#requirement)
 - [APIs](#apis)
 - [SmartLink data format](#smartlink-data-format)
@@ -28,6 +29,11 @@
   - [Android Auto VIP Socket](#android-auto-vip-socket)
   - [CarPlay VIP Socket](#carplay-vip-socket)
 
+## Purpose
+<pre>
+SmartLink is a middleware about IPC between applications.
+</pre>
+
 ## Requirement
 - Platform: STA5