Merge pull request #18367 from thaJeztah/zelahi-17586-systemd-documentation

[carry] configuring DNS options on systemd

docs/installation/ubuntulinux.md

@@ -349,6 +349,12 @@ To avoid this warning, you can specify a DNS server for use by Docker
 containers. Or, you can disable `dnsmasq` in NetworkManager. Though, disabling
 `dnsmasq` might make DNS resolution slower on some networks.
 
+The instructions below describe how to configure the Docker daemon
+running on Ubuntu 14.10 or below. Ubuntu 15.04 and above use `systemd`
+as the boot and service manager. Refer to [control and configure Docker
+with systemd](../articles/systemd.md#custom-docker-daemon-options) to
+configure a daemon controlled by `systemd`.
+
 To specify a DNS server for use by Docker:
 
 1. Log into Ubuntu as a user with `sudo` privileges.