Initial hacker documentation

This is putative hacker documentation and I'm happy to adjust it as necessary to suit the current maintainers.

This was such a good resource in Docker that it would be a shame to lose it. Unfortunately, we can't just link to the corresponding information in the Docker project as a number of aspects are bound to be different here.

I've assumed that libcontainer will have @crosbymichael as a BDFL, so if the maintainers aren't comfortable with that, we'll have to find another decision-making process.

There are also some placeholder (i.e. broken) links. Hope that's ok for now.

Docker-DCO-1.1-Signed-off-by: Glyn Normington <gnormington@gopivotal.com> (github: glyn)
Right. @rjnagal made the same suggestion. I've moved the files to the root, merged the README.md's together, and renamed some files for clarity (e.g. to avoid confusion between MAINTAINERS and MAINTAINERS.md). I don't like a lot of files in the root directory, but maybe it's ok. (If we end up with development scripts, we'll need a subdirectory for them, but no need for that yet.)