Corrected the multiphase flow model equations in the manual.
Corrected the multiphase flow model equations in the manual.

jrper/fluidity,jjo31/ATHAM-Fluidity,jjo31/ATHAM-Fluidity,rjferrier/fluidity,jjo31/ATHAM-Fluidity,rjferrier/fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,jrper/fluidity,rjferrier/fluidity,jrper/fluidity,rjferrier/fluidity,iakovos-panourgias/fluidity,jrper/fluidity,iakovos-panourgias/fluidity,rjferrier/fluidity,iakovos-panourgias/fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity