Add Epiverse integration vignette

The {quickfit} package should provide the glue for simple fitting procedures across Epiverse packages. A vignette outlining how this is done would be useful for users coming to {quickfit} for the first time to see where it may be useful in their package.

**Note**: {quickfit} is developed as a utilities package primarily for packages in [Epiverse-TRACE](https://github.com/epiverse-trace). It is may therefore be tailored more in its development for these packages at the cost of being less general and widely applicable.