Record LAMMPS installation requirements for Ghastly

[ZoeRichter]

LAMMPS is a large program, and only a few select modules/options are needed. Explicitly outlining what features are needed will help users unfamiliar with LAMMPS install it for use with Ghastly. Links to relevant pages in the LAMMPS documentation may also be helpful.

This issue can be closed when there is some sort of documentation (perhaps a README section in the top-level of the lammps-directory) that explicitly mentions necessary modules/installation flags used.

(edited to reflect name change)

[katyhuff]

Add comments to the shell script for now.

[ZoeRichter]

Address README comments from re-circulation pr as checklist so you include them