Add RPi specific cgroup documentation

[spatterIight]

I followed this using 4 RPi Model B's and ran into an issue regarding runc/containerd -- with my pods being stuck in CrashLoopBackOff

The issue was that RPi's require a special cgroups modification to be used w/ kubernetes:

By default the cgroup memory option will be disabled, we will need to update this for Docker to be able to limit memory usage. 
Open /boot/cmdline.txt and append cgroup_enable=memory cgroup_memory=1.

https://alexsniffin.medium.com/a-guide-to-building-a-kubernetes-cluster-with-raspberry-pis-23fa4938d420

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Since this repository is only written with ARM boards in mind (like the RPi) it may be good to add a note about this somewhere, seeing as how popular they are and likely that one may be used.

[chosensamurai]

Thanks a lot for posting this, I was doing exactly this and kept running into the crashloopbackoff thing. Good learning experience though :)

[mattwelke]

Adding a note for anyone else with the particular issue I ran into...

It must be appended. Don't add it as a new line. My file on one of my worker nodes:

console=serial0,115200 console=tty1 root=PARTUUID=84440d60-02 rootfstype=ext4 fsck.repair=yes rootwait cgroup_enable=memory cgroup_memory=1

I was using Raspberry Pi OS Lite 64-bit