feat: add resource for linux service management

Added hands-on resource for Linux service management. LabEx is an excellent guide which explores Linux service management through systemd and systemctl.

src/data/roadmaps/linux/content/108-service-management/index.md

@@ -16,4 +16,8 @@ sudo systemctl start sshd
 sudo systemctl status sshd
 ```
 
-Managing services is a key skill in Linux system administration and essential for maintaining a secure and stable system.
+Managing services is a key skill in Linux system administration and essential for maintaining a secure and stable system.
+
+Learn more from the following resources:
+
+- [@article@How to Master Linux Service Management with Systemctl](https://labex.io/tutorials/linux-how-to-master-linux-service-management-with-systemctl-392864)