Fix typo in the comment about the harmonic bond

tut1_polymer/init.sh

@@ -166,7 +166,7 @@ id type xs ys zs ix iy iz
 # Potentials
 
 # Use harmonic bonds to link between beads for initial equilibration
-# U_harm(r) = k*(r-r_0)
+# U_harm(r) = k*(r-r_0)^2
 bond_style harmonic
 # Key params: bond_type k r_0
 bond_coeff 1 100.0 1.1