Document required variables for each excitation

[mikerouleau]

Document all vars that are used in solver/ are expected to be in input file.

• [ ] click
• [ ] gaussianenvelope
• [ ] raisedsine
• [ ] sine
• [ ] toneburst
• [ ] twotone

[mikerouleau]

All enumerated on dev branch, awaiting descriptions from @geosamaras

[mikerouleau]

Moving to backlog - need participation from the MATLAB model team.

[mikerouleau]

Make sure to also document excitation types