docs: add known issue cross-arch building (#889)

### What does this PR do?

* Adds documentation regarding cross-arch building
* Docs are meant as an intermediary until podman machine is patched with
  the new QEMU calls
* When QEMU is patched, the only thing needed is to "disable rosetta"

### Screenshot / video of UI

<!-- If this PR is changing UI, please include
screenshots or screencasts showing the difference -->

N/A

### What issues does this PR fix or reference?

<!-- Include any related issues from Podman Desktop
repository (or from another issue tracker). -->

References #808

### How to test this PR?

<!-- Please explain steps to reproduce -->

Follow documentation instructions on how to cross-arch build again.

Signed-off-by: Charlie Drage <charlie@charliedrage.com>

README.md

@@ -16,6 +16,8 @@ Easily go from container to VM / ISO-on-a-USB / RAW image!
 - [Requirements](#requirements)
 - [Installation](#installation)
 - [Usage](#usage)
+- [Preferences](#preferences)
+- [Known Issues](#known-issues)
 - [Contributing](#contributing)
 
 ## Technology
@@ -207,6 +209,61 @@ Preferences such as the default `bootc-builder-image` as well as timeouts can be
 
 ![](https://raw.githubusercontent.com/containers/podman-desktop-extension-bootc/main/docs/img/preferences.png)
 
+## Known issues
+
+**Unable to build cross-arch images on macOS and Windows:**
+
+This is a [known issue](https://github.com/containers/podman-desktop-extension-bootc/issues/808) when attempting to build cross-architecture images using Podman Machine on macOS and Windows. For example, building an x86 image on macOS with Apple Silicon (ARM).
+
+The issue stems from a missing [openat2](https://www.mail-archive.com/qemu-devel@nongnu.org/msg1064233.html) system call in QEMU, which has now been patched upstream. While waiting for the patch to be incorporated into Podman Machine, Fedora packages have been created to address the issue.
+
+Your Podman Machine might not have the required QEMU patch to build cross-architecture images.
+
+**macOS only**:
+
+1. Delete your current Podman Machine via **Settings > Resources > Podman**.
+2. Disable Rosetta under **Settings > Preferences > Extension: Podman > Rosetta**.
+3. Create a new Podman Machine.
+
+**Windows and macOS**:
+
+1. Start your Podman Machine.
+2. SSH into the Podman Machine:
+
+```sh
+$ podman machine ssh
+```
+
+3. Override the QEMU binaries:
+
+If your host machine is x86 (AMD64), run:
+
+```sh
+$ rpm-ostree override replace https://download.copr.fedorainfracloud.org/results/michaelvogt/qemu-user-with-openat2/fedora-40-x86_64/08033635-qemu/qemu-user-8.2.6-3.mvo1.fc40.x86_64.rpm 
+$ rpm-ostree override replace https://download.copr.fedorainfracloud.org/results/michaelvogt/qemu-user-with-openat2/fedora-40-x86_64/08033635-qemu/qemu-user-static-aarch64-8.2.6-3.mvo1.fc40.x86_64.rpm
+```
+
+If your host machine is ARM (ARM64), run:
+
+```sh
+$ rpm-ostree override replace https://download.copr.fedorainfracloud.org/results/michaelvogt/qemu-user-with-openat2/fedora-40-aarch64/08033635-qemu/qemu-user-8.2.6-3.mvo1.fc40.aarch64.rpm 
+$ rpm-ostree override replace https://download.copr.fedorainfracloud.org/results/michaelvogt/qemu-user-with-openat2/fedora-40-aarch64/08033635-qemu/qemu-user-static-x86-8.2.6-3.mvo1.fc40.aarch64.rpm
+```
+
+4. Restart your Podman Machine:
+
+```sh
+$ podman machine stop
+$ podman machine start
+```
+
+To undo the fix, either delete and re-create the Podman Machine, or:
+
+```sh
+$ podman machine ssh
+$ rpm-ostree override reset --all
+```
+
 ## Contributing
 
 Want to help develop and contribute to the bootc extension? View our [CONTRIBUTING](https://github.com/containers/podman-desktop-extension-bootc/blob/main/CONTRIBUTING.md) document.