docs: add set up runner (#829)

docs/en/setup_runner.md

+# Set up self hosted runner for GitHub Action
+
+## Config Runner
+
+```bash
+# https://github.com/sgl-project/sglang/settings/actions/runners/new?arch=x64&os=linux
+# Involves some TOKEN and other private information, click the link to view specific steps.
+```
+
+## Start Runner
+
+add `/lib/systemd/system/runner.service`
+```
+[Unit]
+StartLimitIntervalSec=0
+[Service]
+Restart=always
+RestartSec=1
+ExecStart=/home/lmzheng/zhyncs/actions-runner/run.sh
+[Install]
+WantedBy=multi-user.target
+```
+
+```bash
+sudo systemctl daemon-reload
+sudo systemctl start runner
+sudo systemctl enable runner
+sudo systemctl status runner
+```