lavf/segment: move file description to @file doxy

libavformat/segment.c

@@ -1,5 +1,4 @@
 /*
- * Generic segmenter
  * Copyright (c) 2011, Luca Barbato
  *
  * This file is part of Libav.
@@ -19,6 +18,10 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+/**
+ * @file generic segmenter
+ */
+
 #include <float.h>
 
 #include "avformat.h"