Update README.md

Signed-off-by: Glenn Fiedler <glenn@networknext.com>

Author: gafferongames

README.md

@@ -4,6 +4,8 @@
 
 **reliable** is a simple packet acknowledgement system for UDP-based protocols.
 
+It's useful in situations when you need to know which UDP packets you sent are received by the other side.
+
 ![image](https://github.com/mas-bandwidth/reliable/assets/696656/c58edcde-8bff-4683-8bc9-36c562ee7570)
 
 It has the following features: