Linux Kernel Markers: document format string

Describes the format string standard further: Use of field names before the
type specifiers..

Signed-off-by: Mathieu Desnoyers <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/markers.txt

···
 
 And,
 
-trace_mark(subsystem_event, "%d %s", someint, somestring);
+trace_mark(subsystem_event, "myint %d mystring %s", someint, somestring);
 Where :
 - subsystem_event is an identifier unique to your event
     - subsystem is the name of your subsystem.
     - event is the name of the event to mark.
-- "%d %s" is the formatted string for the serializer.
+- "myint %d mystring %s" is the formatted string for the serializer. "myint" and
+  "mystring" are repectively the field names associated with the first and
+  second parameter.
 - someint is an integer.
 - somestring is a char pointer.