Update build to run qemu on MacOS

README.md

@@ -13,11 +13,13 @@ kernel heap. See [`docs/`](docs/README.md) for how each piece works.
   versions are rejected, because Zig makes breaking changes between releases
   pre-1.0. A toolchain manager such as [zvm](https://github.com/tristanisham/zvm)
   or `zigup` will pick up `.zig-version` automatically.
-- **QEMU** (`qemu-system-x86_64`) — to run and test the kernel.
+- **QEMU** (`qemu-system-x86_64`) — to run and test the kernel. On macOS,
+  `brew install qemu` also bundles the OVMF firmware below.
 - **OVMF** UEFI firmware — the `edk2-ovmf` package (Arch), `ovmf` (Debian/Ubuntu),
-  or `edk2-ovmf` (Fedora). The build defaults to the Arch paths
-  (`/usr/share/edk2/x64/OVMF_{CODE,VARS}.4m.fd`); override with `-Dovmf-code=` and
-  `-Dovmf-vars=` if your distro installs them elsewhere.
+  or `edk2-ovmf` (Fedora); on macOS it ships inside the Homebrew `qemu` formula.
+  Both the build and the test harness probe the known Arch/Debian/Fedora/macOS
+  layouts and use the first that exists, so no configuration is normally needed.
+  Override with `-Dovmf-code=` / `-Dovmf-vars=` (build) if yours lives elsewhere.
 - **Python 3** — for the QEMU integration test harness.
 
 ## Build