Update documentation with backup compression
Update documentation with backup compression

Fixes #7456

Signed-off-by: Johan Ehnberg <759412786bc533369b22377bf83fb9056c5b25b2@molnix.com>

Skarlso/lxd,atxwebs/lxd,atxwebs/lxd,atxwebs/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,hallyn/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,lxc/lxd,mjeanson/lxd,Skarlso/lxd,stgraber/lxd,Skarlso/lxd,hallyn/lxd,atxwebs/lxd,Skarlso/lxd,stgraber/lxd,lxc/lxd,mjeanson/lxd,lxc/lxd,mjeanson/lxd