Clarify meaning of --print-moves in hroller man page

Clarify meaning of --print-moves in hroller man page

When given the option --print-moves, hroller prints a list of
instance relocations after each reboot group. This sequential
presentation can lead to the wrong impression, that these are
all the moves to be carried out. Therefore, explicitly mention
the assumption that after each reboot of a group, all instances
are moved to their initial position.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>