Add some comments for the line clear

Author: bill88t

main.c

@@ -299,6 +299,10 @@ STATIC bool maybe_run_list(const char *const *filenames, size_t n_filenames) {
     if (_current_executing_filename == NULL) {
         return false;
     }
+
+    // This function is used for `boot.py` and is then logged into `boot_out.txt`.
+    // We do not want the line clear to be logged.
+    // The function `serial_write` is the only function that isn't logged into the file.
     serial_write(line_clear);
     mp_hal_stdout_tx_str(_current_executing_filename);
     serial_write_compressed(MP_ERROR_TEXT(" output:\n"));