docs: further elaborate the limitations and the restarting #224

Job	Run time
GROMACS (release-2023) / test_backends	4m 8s
GROMACS (main) / test_backends	18m 57s
LAMMPS (develop) / test_backends	8m 49s
NAMD (main) / test_backends	6m 59s
VMD / test_backends	1m 37s
	40m 30s

Provide feedback