virsh: Clarify that memtune parameters may be rounded in the man page

AUTHORS

@@ -251,6 +251,8 @@ Patches have also been contributed by:
   Chuck Short          <chuck.short@canonical.com>
   Sebastian Wiedenroth <wiedi@frubar.net>
   Ata E Husain Bohra   <ata.husain@hotmail.com>
+  Jan Tomko            <jtomko@redhat.com>
+
   [....send patches to get your name here....]
 
 The libvirt Logo was designed by Diana Fong

tools/virsh.pod

@@ -1366,7 +1366,10 @@ appropriate limit is adjusted if supported by the hypervisor.  LXC and
 QEMU/KVM support I<--hard-limit>, I<--soft-limit>, and I<--swap-hard-limit>.
 I<--min-guarantee> is supported only by ESX hypervisor.  Each of these
 limits are scaled integers (see B<NOTES> above), with a default of
-kibibytes (blocks of 1024 bytes) if no suffix is present.
+kibibytes (blocks of 1024 bytes) if no suffix is present. Libvirt rounds
+up to the nearest kibibyte.  Some hypervisors require a larger granularity
+than KiB, and requests that are not an even multiple will be rounded up.
+For example, vSphere/ESX rounds the parameter up to mebibytes (1024 kibibytes).
 
 If I<--live> is specified, affect a running guest.
 If I<--config> is specified, affect the next boot of a persistent guest.