io_getevents.2: Clarify details of return value for timeout-expired case

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/io_getevents.2

@@ -51,8 +51,13 @@ events have been obtained.
 .SH RETURN VALUE
 On success,
 .BR io_getevents ()
-returns the number of events read: 0 if no events are
-available, or less than \fImin_nr\fP if the \fItimeout\fP has elapsed.
+returns the number of events read.
+This may be 0, or a value less than
+.IR min_nr ,
+if the
+.I timeout
+expired.
+
 For the failure return, see NOTES.
 .SH ERRORS
 .TP