doc: document the asf demuxer

And drop a typo from the previous FLV entry.

doc/demuxers.texi

@@ -95,8 +95,19 @@ Adobe Flash Video Format demuxer.
 This demuxer is used to demux FLV files and RTMP network streams.
 
 @table @option
-@item -flv_demuxer @var{bool}
+@item -flv_metadata @var{bool}
 Allocate the streams according to the onMetaData array content.
 @end table
 
+@section asf
+
+Advanced Systems Format demuxer.
+
+This demuxer is used to demux ASF files and MMS network streams.
+
+@table @option
+@item -no_resync_search @var{bool}
+Do not try to resynchronize by looking for a certain optional start code.
+@end table
+
 @c man end INPUT DEVICES