small format fix4

additional-ip-in-linux.mdx

@@ -18,7 +18,16 @@ you want to add the secondary IP of `192.168.1.2` as follows
 **edit** `/etc/network/interfaces` and  
 **add** the following 2 lines at the end of your config:
 
-    auto eth0 iface eth0 inet static   address 192.168.1.1   netmask 255.255.255.0   gateway 192.168.1.254 post-up ip a a 192.168.1.2/24 dev eth0 pre-down ip a d 192.168.1.2/24 dev eth0
+```bash
+    auto eth0
+    iface eth0 inet static
+        address 192.168.1.1
+        netmask 255.255.255.0
+        gateway 192.168.1.254
+
+    post-up ip a a 192.168.1.2/24 dev eth0
+    pre-down ip a d 192.168.1.2/24 dev eth0
+```
 
 After editing, run the command `sudo ifup eth0:0` to activate the new interface.