README

TO DO:

-Langevin function needs to calculate bias potential as well as provided PES object (so need to call cen_diff_deriv with variables for mean/std_dev & height of Gaussians)
-need to scale height of Gaussians appropriately (e.g. for well-tempered MTD)
-need to incorporate random seeds, wt (well-tempering), and timestep variables properly
-need to print walker information to output files