mkdocs and aws need a /index.html, so I moved the introdcution/home.md t...

...o index.md, and renamed the section to About - Introduction is difficult - its often used to introduce the documentation set, rather than what this does - introduce Docker.

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)