[CIG-MC] mgunit, levels README correction

[Ethan Fahy]

Hello everyone,

After looking at the README file for CitcomCU and trying several runs
to verify, it looks like the documentation is off a bit when
describing the number of elements in each direction.

"The next four parameters specify the total number of elements for
the calculation with multigrid solver. The first three give the
base level grid in each direction, and the fourth parameter "levels"
indicates how many times it gets doubled. For example, in the sample
input file input1, mgunitx=6,mgunitz=6,mgunity=6,levels=4, and the
total number of elements in each direction are 48, i.e., grid size
of 48x48x48. "  --from README

If the mgunit value of 6 is doubled 3 times you'd get 48, not 4 times.
 I think that "levels - 1" is equal to the number of times that mgunit
is doubled to get the number of elements in a given direction.  After
looking at some output I think this is correct, but please let me know
if I'm missing something here.  Thanks for your time everyone.

-Ethan Fahy