refactor!: Migrate zig from library to example

Since Zig is a compile-time language and the entry contains
simply a "Hello, world!" application it does not make sense
to include it as a standalone entry in the library.

This better serves as an example therefore.  Additional
changes clean up the example.

Signed-off-by: Alexander Jung <alex@unikraft.io>

Author: nderjung

examples/helloworld-zig/Dockerfile

@@ -0,0 +1,31 @@
+FROM gcc:13.2.0-bookworm AS zig
+
+RUN set -xe; \
+    apt-get update; \
+    apt-get install -y --no-install-recommends \
+      ca-certificates \
+      curl \
+      xz-utils;
+
+WORKDIR /zig
+
+ARG ZIG_VERSION=0.11.0
+
+RUN set -xe; \
+    curl -o /zig.tar.xz https://ziglang.org/download/0.11.0/zig-linux-$(uname -m)-${ZIG_VERSION}.tar.xz; \
+    tar -xf /zig.tar.xz --strip-components 1 -C /zig; \
+    mv /zig/zig /usr/bin/zig; \
+    mv /zig/lib /usr/lib/zig
+
+FROM zig AS build
+
+WORKDIR /src
+
+COPY . /src
+
+RUN set -xe; \
+    zig build-exe /src/helloworld.zig -fPIE -static
+
+FROM scratch
+
+COPY --from=build /src/helloworld /helloworld

examples/helloworld-zig/Kraftfile

@@ -0,0 +1,7 @@
+spec: v0.6
+
+runtime: unikraft.org/base:latest
+
+rootfs: ./Dockerfile
+
+args: ["/helloworld"]

examples/helloworld-zig/README.md

@@ -0,0 +1,57 @@
+# Zig "Hello, world!"
+
+This directory contains a Zig-based "Hello, world!" example running on Unikraft.
+
+## Set Up
+
+To run this example, [install Unikraft's companion command-line toolchain `kraft`](https://unikraft.org/docs/cli), clone this repository and `cd` into this directory.
+
+## Run and Use
+
+Use `kraft` to run the image and start a Unikraft instance:
+
+```bash
+kraft run --rm --plat qemu --arch x86_64 .
+```
+
+If the `--plat` argument is left out, it defaults to `qemu`.
+If the `--arch` argument is left out, it defaults to your system's CPU architecture.
+
+Once executed, you should see a "Bye, World!" message.
+
+## Inspect and Close
+
+To list information about the Unikraft instance, use:
+
+```bash
+kraft ps
+```
+
+```text
+NAME            KERNEL                          ARGS         CREATED        STATUS   MEM  PORTS  PLAT
+elastic_goblin  oci://unikraft.org/base:latest  /helloworld  9 seconds ago  running  64M         qemu/x86_64
+```
+
+The instance name is `elastic_goblin`.
+To close the Unikraft instance, close the `kraft` process (e.g., via `Ctrl+c`) or run:
+
+```bash
+kraft rm elastic_goblin
+```
+
+Note that depending on how you modify this example your instance **may** need more memory to run.
+To do so, use the `kraft run`'s `-M` flag, for example:
+
+```bash
+kraft run --rm --plat qemu --arch x86_64 -M 256M .
+```
+
+## `kraft` and `sudo`
+
+Mixing invocations of `kraft` and `sudo` can lead to unexpected behavior.
+Read more about how to start `kraft` without `sudo` at [https://unikraft.org/sudoless](https://unikraft.org/sudoless).
+
+## Learn More
+
+- [How to run unikernels locally](https://unikraft.org/docs/cli/running)
+- [Building `Dockerfile` Images with `BuildKit`](https://unikraft.org/guides/building-dockerfile-images-with-buildkit)

library/zig/0.11.0/helloworld.zig examples/helloworld-zig/helloworld.zig

@@ -1,5 +1,5 @@
 const std = @import("std");
 
 pub fn main() !void {
-    std.debug.print("Hello, World!\n", .{});
+    std.debug.print("Hello, world!\n", .{});
 }