Docs: List extra requirements for use with Raspberry Pi

[Aflynn50]

When running microcloud on a Raspberry Pi (without microovn) the following error message will appear after a cluster is successfully created with microcloud init.

Error: Failed adding link: Failed to run: ip link add name lxdfan0-fan type vxlan id 15728640 dev eth0 local 192.168.0.43 dstport 0 fan-map 240.0.0.0/8:192.168.0.0/24: exit status 2 (Error: Unknown device type.)

The error is appears because the newer Ubuntu RPi kernels don't include the vxlan module (launchpad issue here)

The kernel module needs to be installed an enabled for networking in lxd cluster containers to work properly.

To enable the vxlan module:

• apt install linux-modules-extra-raspi
• reboot
• modprobe vxlan

This should be documented somewhere in the microcloud documentation.