Added arXiv link

git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@12511 f3b2605a-c512-4ea7-a41b-209d697bcdaa
git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@12512 f3b2605a-c512-4ea7-a41b-209d697bcdaa