docs: document how to write @varargs in kernel-doc

Add documentation on how to use kernel-doc for function parameters
that are "..." (varargs).
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/kernel-doc-nano-HOWTO.txt

@@ -71,6 +71,11 @@ The @argument descriptions must begin on the very next line following
 this opening short function description line, with no intervening
 empty comment lines.
 
+If a function parameter is "..." (varargs), it should be listed in
+kernel-doc notation as:
+ * @...: description
+
+
 Example kernel-doc data structure comment.
 
 /**