新增说明文件；新增Docker、Redis、Tomcat示例

examples/docker.service

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+[Unit]
+Description=Docker Application Container Engine
+Documentation=https://docs.docker.com
+After=network-online.target firewalld.service
+Wants=network-online.target
+Requires=docker.socket
+
+[Service]
+Type=notify
+Environment=PATH=/opt/docker/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+# the default is not to use systemd for cgroups because the delegate issues still
+# exists and systemd currently does not support the cgroup feature set required
+# for containers run by docker
+ExecStart=/opt/docker/bin/dockerd -H unix://var/run/docker.sock
+ExecReload=/bin/kill -s HUP
+# Having non-zero Limit*s causes performance problems due to accounting overhead
+# in the kernel. We recommend using cgroups to do container-local accounting.
+LimitNOFILE=infinity
+LimitNPROC=infinity
+LimitCORE=infinity
+# Uncomment TasksMax if your systemd version supports it.
+# Only systemd 226 and above support this version.
+#TasksMax=infinity
+TimeoutStartSec=0
+# set delegate yes so that systemd does not reset the cgroups of docker containers
+Delegate=yes
+# kill only the docker process, not all processes in the cgroup
+KillMode=process
+# restart the docker process if it exits prematurely
+Restart=on-failure
+StartLimitBurst=3
+StartLimitInterval=60s
+
+[Install]
+WantedBy=multi-user.target