Need to think about how to apply this for subgroups
plot_km_pi(km.pi, show.obs = TRUE, trunc.sim.censor = TRUE)an output from calc_km_pi function.
A logical specifying whether to show observed K-M curve on the plot.
This will have no effect if `calc.obs` was set to `FALSE` in calc_km_pi.
A logical specifying whether to truncate the simulated
curve at the last time of `censor.dur`` specified in surv_param_sim.