sdk: Add contributors to AUTHORS.md

This patch adds the names of contributors to the AUTHORS.md file. The
list has been extracted from the output of git log.

Change-Id: Ia8e709d5faa77691c717e977ce974bee50318ef1
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>
(cherry picked from commit 2502a8fda6f54af3c63c7506dd2675cd9135bbde)