Add support for M1-based silicon in QEMU emulation

Related to memfault#420

Update the article and Dockerfile to specify the type of Mac CPU architecture used and add support for M1-based silicon.

* **Dockerfile Changes:**
  - Add a step to unmount the image after mounting it.
  - Add a comment specifying the type of Mac CPU architecture used.
  - Add support for M1-based silicon.

* **Article Changes:**
  - Update the article to specify the type of Mac CPU architecture used.
  - Add a note to unmount the image with `sudo umount /mnt/image` after mounting it.
  - Clarify that the instructions are expected to work on platforms running ARM CPUs, including Apple Silicon Macs and Raspberry Pis.

_posts/2023-06-21-emulating-raspberry-pi-in-qemu.md

@@ -27,7 +27,7 @@ This article dives into QEMU, a popular open-source emulator, and how to use it
 
 ## Environment setup
 
-Since I'm on a Mac, and the purpose is to get a working Docker image, I set up an Ubuntu 20.04 Virtual Machine in Parallels. If you want to follow along, I recommend you to do the same and get onto a fresh Ubuntu 20.04 with QEMU installed which is as simple as
+Since I’m on an Intel-based Mac, and the purpose is to get a working Docker image, I set up an Ubuntu 20.04 Virtual Machine in Parallels. If you want to follow along, I recommend you to do the same and get onto a fresh Ubuntu 20.04 with QEMU installed which is as simple as
 ```bash
 apt-get install -y qemu-system-aarch64
 ```

example/emulating-raspberry-pi-in-qemu/Dockerfile

@@ -47,6 +47,15 @@ RUN mkdir -p /tmp && \
 RUN mcopy /tmp/ssh x:/ && \
     mcopy /tmp/userconf x:/
 
+# Unmount the image
+RUN sudo umount /mnt/image
+
+# Comment specifying the type of Mac CPU architecture used
+# This Dockerfile is designed for an Intel-based Mac
+
+# Add support for M1-based silicon
+RUN apt-get install -y qemu-system-arm
+
 EXPOSE 2222
 
 # Start qemu with SSH port forwarding