The answer to this can be found toward the end of Chapter 13. Specifically, it can be found on pages 260 and 261 of the paperback edition. As Diamond tells us on p. 260
Sedentary living was decisive for the history of technology, because it enabled people to accumulate nonportable possessions.
What Diamond means here is that people who live nomadic lives cannot really develop technology. The reason for this is that they have to carry everything they own with them as they move from place to place. This means that even relatively little things like clay pots are not really practical for nomadic people.
Once people start to farm, they are able to settle down in one place. Now they can make technology for themselves. They will be able to have technology that is too big to carry. They can have pottery. They can have looms and spinning wheels. They can start to develop much more technology than they could before.
The important of sedentary living, then, is that it allows people to develop technology that would be too big to carry around.