Notation in Markov chain lecture

[jstac]

@HumphreyYang , some code uses n as the number of simulations or initial conditions.

It's better if we reserve n for the size of the state space, to be consistent with the maths.

Also, innp.empty((n, P.shape[0])) the term P.shape[0] should be n_state

(But n_state should be changed to n after the number of initial conditions is counted with a different integer.`)

Could you please make these fixes? Thanks in advance.