Target audience specific parameters

[n8thangreen]

The name, vignette and functionality should cater to that target audience, particularly when it comes to those two additional steps. Firstly, the parameters required for the copula covariate simulation in G-computation/MIM should be arguments to the main function: summary statistics (e.g. the means/proportions and potentially the standard deviations) of the marginal distributions and the marginal distribution forms (e.g. normal, log-normal, gamma, etc). This should also be featured in the vignette.