Document how relocatability is achieved

[alexpdp7]

I'm not familiar with the structure of the project, so I went poking for the trick, but I couldn't find it. I assume you do some kind of chroot/proot depending on which platform you are on?

It would be interesting to be upfront about how this is done, because the specific tricks might not be available in some environments (e.g. I do a lot of dev work inside an LXC container, so there are many stuff which I cannot use).