qemu-option-trace: -trace enable= is a pattern, not a file

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

qemu-option-trace.texi

@@ -2,9 +2,8 @@ Specify tracing options.
 
 @table @option
 @item [enable=]@var{pattern}
-Immediately enable events matching @var{pattern}.
-The file must contain one event name (as listed in the @file{trace-events-all}
-file) per line; globbing patterns are accepted too.  This option is only
+Immediately enable events matching @var{pattern}
+(either event name or a globbing pattern).  This option is only
 available if QEMU has been compiled with the @var{simple}, @var{log}
 or @var{ftrace} tracing backend.  To specify multiple events or patterns,
 specify the @option{-trace} option multiple times.