add the term "attack rate" as familiar with target audience

hi @amanda-minter do you find it appropriate to add it to these lines?

- final size in https://epiverse-trace.github.io/tutorials-late/model-choices.html#available-models-in-epidemics

```
which can then be used to calculate the attack rate or final size of the epidemic
```

- final epidemic size in https://epiverse-trace.github.io/tutorials-late/compare-interventions.html#calculating-outcomes-averted

```
This function calculates the attack rate or final epidemic size for each scenario,
```