fix(docs): update installation steps for windows and linux

[profnandaa]

This PR updates the installation instructions for Windows and Linux.

We didn't have Windows installation steps and the Linux one was using brew (needs another extra installation);
sort of an anti-pattern from how we install the rest of the ecosystem tools like containerd, etc.

[profnandaa]

ctr run works okay but getting this when I run nerdctl run, let me fix that and update the README too:

nerdctl run --rm -it mcr.microsoft.com/windows/nanoserver:ltsc2022 cmd
time="2023-03-20T04:32:35Z" level=fatal msg="failed to create default network: needs CNI plugin \"nat\" to be installed in CNI_PATH (\"C:\\\\Program Files\\\\containerd\\\\cni\\\\bin\"), see https://github.com/containernetworking/plugins/releases: exec: \"C:\\\\Program Files\\\\containerd\\\\cni\\\\bin\\\\nat\": file does not exist"

[AkihiroSuda]

Why remove?

[profnandaa]

I just renamed to Linux the other items are based on the OS types instead, i.e. Windows, FreeBSD, MacOS.

[jsturtevant]

looks like we lost the On Linux systems you can install nerdctl via [brew](https://brew.sh): below?

[profnandaa]

@jsturtevant -- I've replaced that with the standard installation process on Linux. I don't see a reason to install brew first so that you can install nerdctl when most likely they have already installed containerd, etc. using the standard process of getting the binaries from Github with curl.

[jsturtevant]

I think we should keep brew install instructions and we can add the additional manual process. Then the user can choose what is best for them.

[profnandaa]

@AkihiroSuda -- thanks for the review, going to make the changes.
I finally have nerdctl running but the way I've set up the CNI-plugin is hacky hence I get this warning:

level=warning msg="default network named \"nat\" does not have an internal nerdctl ID or nerdctl-managed config file, it was most likely NOT created by nerdctl"

What is the best way of setting up the CNI plugin for windows?

I was trying to adapt this bash script here (which I think should be done in PowerShell instead, working on that) - https://gist.github.com/profnandaa/e9ab7bd7e069ce2728840b041ce4c300

[aznashwan]

@profnandaa don't worry about that warning message, even if you didn't explicitly ask for network settings for your container, it's due to the fact that nat is the network name nerdctl defaults to on Windows.

This special treatment of the default network is the result of #1538, after which nerdctl can tell whether a network was initially created by itself as the default network by setting a special label on it.

I was trying to adapt this bash script here

That's perfect since it's basically the "reference configuration" which is used in both the containerd CI, as well as being basically 1:1 lifted to be used in the nerdctl CI too.

Although there's basically no reason to worry about that warning message, and I wouldn't necessarily bother mentioning it in the docs, but you could dodge it by opening the network config file shown in nerdctl network list and either:

• renaming that network to something other than nat (NOTE: the type should still stay nat!)
• keep the nat name but add the following line to the top-level of the config:

{
  ...
   // NOTE: this ID field is all you'll really need, and you can invent your own ID if needed.
  "nerdctlID": "d919a100ce6b45524d415d52d088d5817587c6dd8c3691b03b8063c44d043523",
  "nerdctlLabels": {
    "nerdctl/default-network": "true"
  },
  ...
}