sysfs.2: Add a pointer to sysfs(5) to help possibly confused readers

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

man2/sysfs.2

@@ -34,6 +34,14 @@ sysfs \- get filesystem type information
 .PP
 .BI "int sysfs(int " option );
 .SH DESCRIPTION
+.BR "Note" :
+if you are looking for information about the
+.B sysfs
+filesystem that is normally mounted at
+.IR /sys ,
+see
+.BR sysfs (5).
+.PP
 .BR sysfs ()
 returns information about the filesystem types currently present in
 the kernel.