docs(qqbot): clarify comment on file upload guard

gateway/platforms/qqbot/adapter.py

@@ -1812,8 +1812,9 @@ class QQAdapter(BasePlatformAdapter):
         fn = filename.strip().lower()
         if ct == "voice" or ct.startswith("audio/"):
             return True
-        # QQ file uploads have content_type="file" — never treat as voice,
-        # even if the filename has an audio extension.
+        # QQ file uploads have content_type="file".  Without this guard,
+        # any uploaded audio file (e.g. .wav, .mp3) would be misrouted into
+        # the STT pipeline and never be received as a normal file attachment.
         if ct == "file":
             return False
         _VOICE_EXTENSIONS = (