add example using predefined functions in Get started vignette, relates

#145

vignettes/simulist.Rmd

@@ -222,7 +222,28 @@ The `sim_*()` functions, by default, use an excess degree distribution to accoun
 
 ## Using functions for distributions instead of `<epidist>`
 
-It is possible to use an [anonymous function](https://en.wikipedia.org/wiki/Anonymous_function) instead of an `<epidist>` object when specifying the parameters of the delay and contact distributions. We recommend using the `<epidist>` objects but here outline the alternative approach.
+The `contact_distribution`, `infectious_period`, `onset_to_hosp`, `onset_to_death` and `onset_to_recovery` arguments can accept either an `<epidist>` object (as shown above), or can accept a function. It is possible to use a predefined function or an [anonymous function](https://en.wikipedia.org/wiki/Anonymous_function). Here we'll demonstrate how to use both.
+
+### Predefined functions
+
+```{r, sim-outbreak-func}
+contact_distribution <- function(x) dpois(x = x, lambda = 2)
+infectious_period <- function(x) rgamma(n = x, shape = 2, scale = 2)
+onset_to_hosp <- function(x) rlnorm(n = x, meanlog = 1.5, sdlog = 0.5)
+onset_to_death <- function(x) rweibull(n = x, shape = 0.5, scale = 0.2)
+
+outbreak <- sim_outbreak(
+  contact_distribution = contact_distribution,
+  infectious_period = infectious_period,
+  prob_infection = 0.5,
+  onset_to_hosp = onset_to_hosp,
+  onset_to_death = onset_to_death
+)
+head(outbreak$linelist)
+head(outbreak$contacts)
+```
+
+### Anonymous functions
 
 ```{r, sim-outbreak-anon-func}
 outbreak <- sim_outbreak(