add docker guide

server/docker.md

+## Setup Docker on CensOS
+
+### Install
+Require Kernel version: >= 2.6.32-431.
+
+Use `uname -a` to check current kernel version.
+
+Download latest version at: https://get.docker.com/builds/Linux/x86_64/docker-latest
+
+```bash
+cd /usr/local/bin
+wget https://get.docker.com/builds/Linux/x86_64/docker-latest -O docker
+chmod +x docker
+```
+
+### Run docker daemon
+
+Must run as `root`
+
+```bash
+sudo su -
+docker -d &
+```
+
+### Assign non-root access to docker daemon
+
+For example, we need to give `docker` access to user ventura
+
+Step 1: create group `docker`(if not exist)
+
+```bash
+groupadd docker
+```
+
+Step 2: add existing usere to `docker` group
+
+```bash
+usermod -a -G docker ventura
+```
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