Add a @file notice to avio.h.

Originally committed as revision 17625 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/avio.h

@@ -1,5 +1,4 @@
 /*
- * unbuffered io for ffmpeg system
  * copyright (c) 2001 Fabrice Bellard
  *
  * This file is part of FFmpeg.
@@ -21,6 +20,11 @@
 #ifndef AVFORMAT_AVIO_H
 #define AVFORMAT_AVIO_H
 
+/**
+ * @file libavformat/avio.h
+ * unbuffered I/O operations
+ */
+
 #include <stdint.h>
 
 #include "libavutil/common.h"