kamailio-kemi-framework: docs for add tcp alias functions

kamailio-kemi-framework/docs/core.md

@@ -25,10 +25,14 @@ Set the internal flag to add rport parameter to local generated Via header.
 
 `add_tcp_alias(int port)`
 
+Adds a tcp port alias for the current connection (if tcp). Useful if you want to send all the trafic to port_alias through the same connection this request came from (it could help for firewall or nat traversal). When the `aliased` connection is closed (e.g. it is idle for too much time), all the port aliases are removed.
+
 ### KSR.add_tcp_alias_via() ###
 
 `int add_tcp_alias_via()`
 
+Adds the port from the message via as an alias to TCP connection. See `add_tcp_alias(int port)` for more details.
+
 ### void KSR.dbg(...) ###
 
 `void KSR.dbg(str "msg")`