add one paragraph to assess for rate alpha

[avallecam]

After this paragraph:

tutorials-late/learners/files/hands-on.tex

Lines 116 to 121 in c9ccb33

	Values of these rates can be determined from the natural history of the disease.
	For example, if people are on average infectious for 8 days, then in the model,
	1/8 of currently infectious people would recover each day
	(i.e. the rate of recovery, $\gamma=1/8=0.125$).

Add one to assess that the learner needs to get the value of alpha from the latent period (from E to I)