Improve structure and clarity of wording in Getting Started intro vignette.

[jamesmbaazam]

This is quite a technical opening to a 'get started' vignette. Wonder if it would be useful to have an opening use case panel like in finalsize? Maybe something like 'Suppose we observe a series of small outbreak clusters, each arising from a separate external introduction (e.g. spillover event or importation into the region). What are the likely transmission properties of the infection that generated these clusters?'

Originally posted by @adamkucharski in #122 (comment)