Update INSTALL.md
Update INSTALL.md

Added Ubuntu install walkthrough.
parkhyeonghwa/mtools,ces0712/mtools,tomzhang/mtools,parkhyeonghwa/mtools,yaowenqiang/mtools,yaowenqiang/mtools,aerrami/mtools,devkev/mtools,rueckstiess/mtools,gormanb/mtools,aerrami/mtools,devkev/mtools,gormanb/mtools,tomzhang/mtools,gormanb/mtools,devkev/mtools,ces0712/mtools,tomzhang/mtools,yaowenqiang/mtools,ces0712/mtools,aerrami/mtools,rueckstiess/mtools,parkhyeonghwa/mtools