Update installation instructions for Amazon Linux

[Khalian]

Not everyone has a machine/instance lying around with kvm and virt assist. A lot of developers just leverage cloud providers to give them the necessary instances to work it.

This commit improves installation instructions for Amazon Linux 2

[stealthybox]

Thanks for the patch -- this line should ideally just install containerd, not a full install of docker.

There doesn't appear to be a docker or containerd package on a default AmazonLinux 2 system.
*( I only checked with the amazonlinux:2 docker container's default yum repo setup though )

If you add the docker-ce repo directly from docker, it's possible to install the most up-to-date version of containerd from there, just like the CentOS example:

Suggested change

	which containerd || sudo yum install -y docker
	which containerd || ( yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo && yum install -y containerd.io )

[Khalian]

That was precisely the command I ran before and it did not work. Refer to #670.

[stealthybox]

Ah thanks! Sorry about that -- here's a better fix:

Suggested change

	which containerd || sudo yum install -y docker
	amazon-linux-extras enable docker
	yum install -y containerd

I was able to verify this works within an AL2 docker container

[Khalian]

So yes that works. And that would work fine with docker hub stuff. But when I try it with ECR I cant get it to work with just containerd : #673

[Khalian]

Anyways I still applied it.

[stealthybox]

Thanks for making the install uniform for containerd.
Also appreciate the other bug you opened about registry auth.

I'm glad the docker runtime is helping you get around that 👍

[Khalian]

Yea so about that, I think we need some instructions for runtime modes and more commands like ignite pull. I will be happy to write that down, but where should I put it?