Enhance documentation beyond just CNI examples

[nickheyer]

Without reading the name of the repo, one might think this project is a go wrapper for CNI plugins, meant to be used as a plugin to some other Firecracker SDK. There is an unreasonable amount of investigation required to get something working. There are also no examples of standard implementations beyond configuring static network interfaces or CNI network interfaces.

Regarding CNI/Network: It's unjustly implied that developers come stock with CNI plugins properly built / installed on their host systems, or even know where to find them. When they do eventually locate the CNI plugin repo, they will quickly discover that the standard make commands produce un-versioned plugins that are not actually accepted by firecracker/sdk (for those looking, check out the .github workflow in the actual CNI repo and use the commands there though you will only get a few of the plugin files).

So even with the disproportional focus on the networking setup in the sdk readme, it's clearly still very premature and undocumented. Obviously the firecracker official repo is well documented (though lacking structure as it's just a flat folder of markdown files), so at minimum the sdk docs could contain their Go wrappers for the functionality described in the official firecracker docs.

Finally, code comments do not constitute sufficient documentation for large open source projects, outside of an org.