add additional addresses to interface

admin-guide/configuration/basic/networking.md

@@ -133,6 +133,25 @@ networking::connection::ipoib_network:
       transport-mode: 'connected'
 ```
 
+### Additional IP on Interface
+
+Additionally to then normal first IP address on an interface you may also add additional addresses to a given interface:
+
+```
+networking::connections:
+  - psi_network
+
+networking::connection::psi_network:
+  interface_name: 'eno0'
+  ipv4_method: 'auto'
+  ipv6_method: 'disabled'
+  additional_config:
+    ipv4:
+      address1: '192.168.254.254/24'
+```
+For more addresses just increase the counter after `address`.
+
+
 ### Other Connection Types
 
 NetworkManager also supports other types like `wifi`, `vpn`, `bridge`, `vlan`, etc. Note that other types than `ethernet` and `ethernet` have so far not been tested. Please contact us if you managed to set up some other network type or need help to do so.