Added documentation to PDRFoam.

applications/solvers/combustion/PDRFoam/Make/options

...Foam/PDRModels/XiEqModels/basicXiSubXiEq/basicXiSubXiEq.H

...ion/PDRFoam/PDRModels/XiGModels/basicXiSubG/basicXiSubG.H

.../PDRFoam/PDRModels/dragModels/PDRDragModel/PDRDragModel.H

...ers/combustion/PDRFoam/PDRModels/dragModels/basic/basic.H

...on/PDRFoam/PDRModels/turbulence/PDRkEpsilon/PDRkEpsilon.H

...rs/combustion/PDRFoam/XiModels/XiEqModels/Gulder/Gulder.H

...RFoam/XiModels/XiEqModels/SCOPEBlendXiEq/SCOPEBlendXiEq.H

...bustion/PDRFoam/XiModels/XiEqModels/SCOPEXiEq/SCOPEXiEq.H

...bustion/PDRFoam/XiModels/XiEqModels/XiEqModel/XiEqModel.H

...oam/XiModels/XiEqModels/instabilityXiEq/instabilityXiEq.H

...s/solvers/combustion/PDRFoam/XiModels/XiGModels/KTS/KTS.H

...combustion/PDRFoam/XiModels/XiGModels/XiGModel/XiGModel.H

...on/PDRFoam/XiModels/XiGModels/instabilityG/instabilityG.H

...ons/solvers/combustion/PDRFoam/XiModels/XiModel/XiModel.H

...solvers/combustion/PDRFoam/XiModels/algebraic/algebraic.H

...cations/solvers/combustion/PDRFoam/XiModels/fixed/fixed.H

...solvers/combustion/PDRFoam/XiModels/transport/transport.H

.../PDRFoam/laminarFlameSpeed/SCOPE/SCOPELaminarFlameSpeed.H