Document the -loglevel option in the ffmpeg man page.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@20028 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

doc/ffmpeg-doc.texi

@@ -296,6 +296,20 @@ ffmpeg -i in.avi -metadata title="my title" out.flv
 @item -v @var{number}
 Set the logging verbosity level.
 
+@item -loglevel @var{loglevel}
+Set the logging level used by the library.
+@var{loglevel} is a number or a string containing one of the following values:
+@table @samp
+@item quiet
+@item panic
+@item fatal
+@item error
+@item warning
+@item info
+@item verbose
+@item debug
+@end table
+
 @item -target @var{type}
 Specify target file type ("vcd", "svcd", "dvd", "dv", "dv50", "pal-vcd",
 "ntsc-svcd", ... ). All the format options (bitrate, codecs,