convert into full overlay module

Signed-off-by: Christoph Hartmann <chris@lollyrock.com>
update readme

Signed-off-by: Christoph Hartmann <chris@lollyrock.com>
add hardening recipe

Signed-off-by: Christoph Hartmann <chris@lollyrock.com>
fix lint offenses

Signed-off-by: Christoph Hartmann <chris@lollyrock.com>
Merge pull request #6 from TelekomLabs/overlay

Overlay