Update README.md

README.md

@@ -40,8 +40,8 @@ The dataset has several columns:
 The most important of which is the `simulation_time_steps` which is a
 list of length equal to the number of time steps in the
 simulation. Each element on the list is an array with shape
-`(num_particles, 6)` that, on each row, has the position of the
-particle in the x, y and z axis and the velocity of the particle in
+`(num_particles, 6)` that, on each row `i`, has first the
+velocity in the x, y and z axis and secondly the position of the particle `i` in
 the x, y and z axis.
 
 # Dataset columns