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

[avallecam]

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, 

[amanda-minter]

The first line looks good to me. It doesn't make sense to add 'attack rate' in the second line as the function outcomes_averted() does not calculate the attack rate.