Install zip by default,in order to run `make build`.
Add qemu documentation
Spelling fixes.

Spelling fixes in Chapter 2.
README.md: Correcting punctuation
Some changes in Chapter 3
Typo: access -> accessed
Typo: base->lucid32

the box name 'base' is different from 'lucid32' in Vagrantfile, which causes download box twice, one time for 'vagrant add box' another time for 'vagrant up'