The hardcoded `eth0` network interface in the `http20` function doesn't
exist on macOS. It's more reliable to dynamically determine the
appropriate interface, so this change checks what would be used to reach
Cloudflare's public 1.1.1.1 DNS service (yes, another hardcoded thing,
but at least it's common across the Internet) and uses that interface.
For example, on my macOS system, it returns either `en0` (Wi-Fi) or
`en7` (the Ethernet slot on my Thunderbolt dock).
On Linux, this uses the commonly installed `ip route` command from the
[iproute2](https://wiki.linuxfoundation.org/networking/iproute2)
project. The macOS port of some of these utilities is available from
[Homebrew](https://brew.sh) by running `brew install iproute2mac`.
This change also splits the pipeline in the function across multiple
lines per this project's
[Code Style Guide](https://github.com/ohmyzsh/ohmyzsh/wiki/Code-Style-Guide).
* Added a README file for the systemadmin plugin
* Updated formatting of Functions table and split it into
"named" and "unnamed" functions for clarity
* Fixed issue with '|' characters in table by adding them in
<code> stateuents </code>
* Added \ escape characters in front of | characters