tvheadend: added to wiki with setup and fritzbox guide

wiki/linux/netplan.md

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+# Netplan
+
+[Netplan](https://netplan.io) is a utility for configuring the networking of a
+linux system via YAML files.
+
+## Add more IP addresses to a system
+
+In the file `/etc/netplan/50-cloud-init.yaml` create an `addresses:` section
+for a device (for example an ethernet device) and list the IP addresses you
+want to add to the system to it.
+It has to be noted, that the added addresses should be outside of the DHCP
+range of your router.
+An example file will look something like the following lines.
+In this case 4 addresses were added.
+`192.168.178.18/24` is the IP assigned by the DHCP server.
+It has to be noted that this is a special case as the DHCP server assigns this
+address always to the system.
+
+```txt
+network:
+    ethernets:
+        ens18:
+            dhcp4: true
+            addresses:
+                - 192.168.178.18/24
+                - 192.168.178.201/24
+                - 192.168.178.202/24
+                - 192.168.178.203/24
+                - 192.168.178.204/24
+    version: 2
+```
+
+Afterwards netplan has to be restarted by running `sudo netplan apply`.
+The addresses then are assigned to the system.