Section 16.3.2 says:

 include 'project1', 'project2', 'project2/child1'

I think it should probably say:

 include 'project1', 'project2', 'project2:child1'

It might be even nicer if it said:

include 'project1', 'project2', 'project2:child1'
include 'project3'

This way, you'd also illustrate by example that the settings.gradle file
could contain more than one 'include' statement.

Aside:
It would also be nice if the first paragraph in Section 16.3 said:
"...in the multiproject build in the settings.gradle file". Currently
it just refers to the "settings" file. This looses an opportunity
to reinforce where the user needs to look to make the appropriate
configuration changes.