The previously documented location doesn't work anymore and must not be
used. Warning for backports, different branches are in use depending on
the version (v3.2.10 for 1.7, v3.2.5 for 1.6).
Both DeviceAtlas and 51Degrees used to put their building instructions
in the README, representing more than 1/3 of it. It's better to let the
README focus on generic stuff and building procedure and move the DD
docs to their own files.
