add improvements

[avallecam]

• when refering to R0 add link to https://www.nature.com/articles/s41592-020-0822-z for an explanation
• add summary table about intervention objects (pasted below)
• move normalization to end of episode
• add reference about knowledge dependencies and writing clarity in episode on https://epiverse-trace.github.io/tutorials-late/contact-normalization.html
• add https://www.nature.com/articles/s41592-020-0822-z and http://prism.edu.au/publications/prism-modeling-guideline/ according to the time before reading episode on simulating tranmission

## **Summary**: Intervention objects

In {epidemics} different interventions require different functions, arguments, and R class objects: **integers**, **matrices**, or **lists**.

| Intervention     | Function          | type         | reduction / nu                          | Argument in model_default()                              |
|-------------------|--------------------|--------------|--------------------------------------------|--------------------------------------------------------------|
| Reduce rate       | intervention()     | *"rate"*     | reduction = 0.163                          | intervention = list(*transmission_rate* = \<intervention>)   |
| Reduce contacts   | intervention()     | *"contacts"* | reduction = **matrix**(c(0.5, 0.01, 0.01)) | intervention = list(*contacts* = \<intervention>)             |
| Vaccination       | ***vaccination()*** | ------------ | nu = **matrix**(c(0.0006, 0.004, 0.02))    | ***vaccination*** = \<intervention>                           |

The **list()** class object helps accepting multiple **consecutive** or **overlapping** interventions in the same simulation.