doc: add arm macOS depends platform triplet

depends/README.md

@@ -29,6 +29,7 @@ Common `host-platform-triplet`s for cross compilation are:
 - `x86_64-pc-linux-gnu` for x86 Linux
 - `x86_64-w64-mingw32` for Win64
 - `x86_64-apple-darwin` for macOS
+- `arm64-apple-darwin` for ARM macOS
 - `arm-linux-gnueabihf` for Linux ARM 32 bit
 - `aarch64-linux-gnu` for Linux ARM 64 bit
 - `powerpc64-linux-gnu` for Linux POWER 64-bit (big endian)