Merge branch 'add_first_step' into 'main'

README.md

samples/README.md

samples/UHFk/README.md

samples/UHFk/first_step/README.md

samples/UHFk/first_step/coulombintra.dat

samples/UHFk/first_step/geom.dat

samples/UHFk/first_step/input.toml

samples/UHFk/first_step/reference/eigen.npz

samples/UHFk/first_step/reference/energy.dat

samples/UHFk/first_step/reference/green.npz

samples/UHFk/first_step/stan.in

samples/UHFk/first_step/transfer.dat

samples/UHFr/README.md

samples/UHFr/first_step/README.md

samples/UHFr/first_step/coulombintra.def

samples/UHFr/first_step/geometry.dat

samples/UHFr/first_step/greenone.def

samples/UHFr/first_step/input.toml

samples/UHFr/first_step/reference/energy.dat

samples/UHFr/first_step/reference/green.dat