add overview comment for package

kcp.go

@@ -1,4 +1,3 @@
-// Package kcp - A Fast and Reliable ARQ Protocol
 package kcp
 
 import (

sess.go

@@ -1,3 +1,10 @@
+// Package kcp-go is a reliable-udp library for golang.
+//
+// This library intents to provide a smooth, resilient, ordered,
+// error-checked and anonymous delivery of streams over UDP packets.
+//
+// The interfaces of this package aims to be compatible with
+// net.Conn in standard library, but offers powerful features for advanced users.
 package kcp
 
 import (