man/io_uring_prep_timeout: add mention of version that added multishot

Link: #959
Signed-off-by: Jens Axboe <[email protected]>

man/io_uring_prep_timeout.3

@@ -57,7 +57,7 @@ The request will return multiple timeout completions. The completion flag
 IORING_CQE_F_MORE is set if more timeouts are expected. The value specified in
 .I count
 is the number of repeats. A value of 0 means the timeout is indefinite and can
-only be stopped by a removal request.
+only be stopped by a removal request. Available since the 6.4 kernel.
 .PP
 The timeout completion event will trigger if either the specified timeout
 has occurred, or the specified number of events to wait for have been posted