Update sonic.md

docs/en/unit/sonic.md

@@ -8,18 +8,23 @@
 
 **Ultrasonic** is an ultrasonic distance measuring sensor unit, with the capability of simultaneous reception and transmission. The ultrasonic probe has a sound frequency of 40KHz, a direction angle of ±20 ° and an accuracy of 1mm. The internal part is calculated by an RCWL-9600 ultrasonic distance measuring chip, and the measurement results can be directly obtained through IIC interface (0x57). The effective distance is 20-1500mm.
 
-### Product Features
+## Product Features
 
 - Split transceiver
 - Effective distance 20-1500mm
 - Wide angle range
 - IIC communication, result output directly
 
-### Includes
+## Includes
 
 - 1x Ultrasonic Unit
 - 1x Grove Cable(20cm)
 
+## Application
+
+- Measuring distance
+- Avoid obstacles
+
 ## Specification
 
 <table>