External laser envelope for time propagation

[aradi]

Is your feature request related to a problem? Please describe.

Related to #1175,

Describe the solution you'd like

• The FromFile {} option being documented

• The code should be able to deal with the first comment line when reading in laser.dat, so such files generated by DFTB+ can be handled without having to delete the first line.

[aradi]

@fbonafe @charlymedrano7 Are you aware of any reasons, this had not been documented so far?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs.