Add initial doc for pwgrid_02
Add initial doc for pwgrid_02

f-fathurrahman/ffr-ElectronicStructure.jl,f-fathurrahman/ffr-ElectronicStructure.jl,f-fathurrahman/ffr-ElectronicStructure.jl,f-fathurrahman/ffr-ElectronicStructure.jl,f-fathurrahman/ffr-ElectronicStructure.jl