[#388] Added warning that the Tenant API is only available since 0.6.
[#388] Added warning that the Tenant API is only available since 0.6.

Signed-off-by: Karsten Frank <22534dcdeefa21bf02bac7694b065eeae56646bb@bosch-si.com>

dejanb/hono,dejanb/hono,dejanb/hono