Update README.md

Author: nishimura5

docs/README.md

@@ -58,3 +58,10 @@ Example is below.
 | 2024-10-24 17:30:32 | 0:04:00 | MEMBER1 | TASK B |
 | 2024-10-24 17:35:32 | 0:09:00 | MEMBER1 | TASK C |
 | ...    | ...     | ...     | ...      |
+
+Sound file
+The timer application will load a 3-second wav file and play it as an alarm. The wav file will be stored in the “sound” folder with the following file name.
+
+ - countdown3_orange.wav
+ - countdown3_cyan.wav
+ - countdown3_lightgreen.wav