[fix] fatal: repository '/root/searx' does not exist

The $SERVICE_USER (searx) needs read permission to clone repository.  The
installation script stops if permission is not granted.

- https://github.com/asciimoo/searx/pull/1803#issuecomment-616406528



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>