Add target docs for aarch64-apple-darwin (M1/M2 macs)

src/doc/rustc/src/platform-support.md

@@ -86,7 +86,7 @@ so Rustup may install the documentation for a similar tier 1 target instead.
 
 target | notes
 -------|-------
-`aarch64-apple-darwin` | ARM64 macOS (11.0+, Big Sur+)
+[`aarch64-apple-darwin`](platform-support/aarch64-apple-darwin.md) | ARM64 macOS (11.0+, Big Sur+)
 `aarch64-pc-windows-msvc` | ARM64 Windows MSVC
 `aarch64-unknown-linux-musl` | ARM64 Linux with musl 1.2.3
 `arm-unknown-linux-gnueabi` | ARMv6 Linux (kernel 3.2, glibc 2.17)

src/doc/rustc/src/platform-support/aarch64-apple-darwin.md

@@ -0,0 +1,41 @@
+# `aarch64-apple-darwin`
+
+**Tier: 2 with host tools**
+
+64-bit Arm-based Apple devices running macOS: Macs with M1-family or later Apple Silicon CPUs.
+
+## Target maintainers
+
+- ???
+
+## Requirements
+
+This target supports host tools and cross-compilation. It provides the full standard library including std and alloc.
+
+Binaries built for this target expect a Apple Silicon Mac on macOS 11.0 Big Sur+.
+
+### Format
+
+The default binary format is Mach-O, the executable format used on Apple's platforms.
+
+## Building the target
+
+Just add it to the `target` with:
+```sh
+rustup target add aarch64-apple-darwin
+```
+
+## Building Rust programs
+
+Rust ships pre-compiled artifacts for this target or build your own copy of `core` by using
+`build-std`.
+
+## Testing
+
+Binaries produced for this target can be run directly on Apple Silicon Macs natively.
+The Rust test suite can be run for this target on such hardware.
+
+## Cross-compilation toolchains and C code
+
+This target supports C code. To build compatible C code, you should use a toolchain targeting aarch64-apple-darwin, such as Xcode on a Mac or GCC.
+The toolchain target triple matches this Rust target triple.