Fix links and unclosed <blockquote> in hw3 instructions

This should fix the links for home (at top-right corner) and QEMU setup on the hw3 instructions page, as well as an unclosed <blockquote> causing the indentation to shift before "Firmware and the BIOS". I also made a slight grammar change and synced the earlier commit today ("Fix segment values, 0x8 and 0x16").