Merge pull request nervosnetwork#4238 from eval-exec/exec/fix-systemd…

…-journalctl

Fix using `journalctl` to check the log of `ckb.service`

devtools/init/linux-systemd/README.md

@@ -58,10 +58,16 @@ Start the node automatically on boot if you like:
 sudo systemctl enable ckb.service
 ```
 
+Check ckb's status:
+
+```bash
+sudo systemctl status ckb.service
+```
+
 If ckb doesn't seem to start properly you can view the logs to figure out the problem:
 
 ```bash
-journalctl --boot -u ckb.service
+sudo journalctl --boot -u ckb.service
 ```
 
 Following the similar instructions to start a miner: