add comments about load balancing granular sims and typo in qb biseg

|                   | in the ParticleBoxArray if dual_grid is true.                         |             |              |

+-------------------+-----------------------------------------------------------------------+-------------+--------------+

Note that when running a granular simulation, i.e., no fluid phase, :cpp:`mfix.dual_grid` must be 0. Hence, 

the :cpp:`particles.max_grid_size` (in each direction) have no meaning. Therefore the fluid grid and tile 

sizes should be set for particle load balancing. It may also be necessary to set the blocking factors to 1. 

The following inputs must be preceded by "mfix" and determine how we load balance:

+----------------------+-----------------------------------------------------------------------+-------------+--------------+

and ceramic 

(:math:`d_p = 4.25` mm, :math:`\rho_p = 2580` kg/m\ :sup:`3` \)

particles. When fluidized, the smaller, lighter nylon particles 

(:math:`U_{mf} ~ 1.1` m/s) segregate out of the mixture to the top, 

with the larger, heavier ceramic particles  (:math:`U_{mf} ~ 1.8` m/s)

(:math:`U_{mf} \approx 1.1` m/s) segregate out of the mixture to the top, 

with the larger, heavier ceramic particles  (:math:`U_{mf} \approx 1.8` m/s)

remaining at the bottom. The batch segregation test was conducted in 

a small bed with a square cross-section of side length 60.325 mm. 

Similar to previous observations of fluidized segregation of