update vignette text

vignettes/epichains.Rmd

@@ -48,11 +48,12 @@ This function calculates the likelihood/loglikelihood of observing a vector of o
 `likelihood()` requires a vector of chain summaries (sizes or lengths),
 `chains`, the corresponding statistic to calculate, `statistic`, the offspring
 distribution, `offspring_dist` and its associated parameters. `offspring_dist`
-is specified as the "base name" of the inbuilt distributions in R, for example,
-"pois", "nbinom", etc. `likelihood()` also requires `nsim_offspring`, which is the
-number of simulations to run if the likelihoods do not have a closed-form
-solution and must be simulated. This argument will be explained further in
-the next section.
+is specified as the function that is used to generate random numbers, i.e.
+`rpois` for Poisson, `rnbinom` for negative binomial, or a custom function. If no
+the closed-form solution is available then simulated replicates are used to
+estimate the likelihoods. In that case `likelihood()` also requires
+`nsim_offspring`, which is the number of simulations to run . This argument will
+be explained further in the next section.
 
 By default, the result is a log-likelihood but if `log = FALSE`, then
 likelihoods are returned.