DEVELOPERS: add initial list of Buildroot developers

This is an initial list of Buildroot developers. It has been created
semi-automatically by parsing the Git history, and finding the authors
of commits with a title like "<foo>: new package". Some additional
manual tweaking has been done (merging multiple entries corresponding to
the same person, adding some more entries, etc.).

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>