Update README.md

README.md

@@ -38,6 +38,9 @@ Functions I wrote and their purpose:
                   the message_data is created following the appropriate data 
                   structure depending on message_type. Then call the correct
                   function inputting the message_data. 
+                
+                returns: 0 if the packet was successfully read
+                         -1 if the packet has invalid data type or message_type
 
 
 - void display_message(char* message, uint16_t message_length):