more detailed comments in uart.c

uart.c

@@ -46,7 +46,7 @@ void read_sync(char buffer[], uint8_t buffersize, uint8_t * bufferindex){
         buffer[*bufferindex]=input;
         *bufferindex=*bufferindex+1;
     }while(!(input == '\n' || input == '\r'));
-    buffer[*bufferindex]=0;
+    buffer[*bufferindex]=0; // null terminate
     putchar('\n');
 }