use `simple-analysis.Rmd` to explore log-linear model advantages and limitations

I think we can later use the `simple-analysis.Rmd` file to still showcase the log-linear model more explicitly with all the assumptions and limitations before introducing EpiNow2. Assumptions and limitations and deciding why to choose a model are easier to interiorize than methods and possibly a more useful message.

_Originally posted by @avallecam in https://github.com/epiverse-trace/tutorials-early/pull/86#pullrequestreview-2132943693_