Review shiny / CI CD / renv / private dependencies

[Chargothrond]

While #14 put github actions in the foreground instead of travis CI, there is still some further restructuring to consider:

• The shiny CI CD chapter has grown and it makes sense to try to split different topics better.
• The part about renv could be extended, leveraging on what we did in the Covid19 app and what was discussed / described in Location of option() statement when using {renv}. #17
• The information about the private / non-CRAN dependencies can also be formulated more clearly which will take care of private non-CRAN dependencies for Shiny app (w/ {renv} + Docker) #18 apart from the Docker component.
  • Open question: Should we consider to include information about Docker in the context of private repos for shiny apps?