Document how to create a fat binary for Mac x86_64 and Apple Silicon (#1636)

* Document how to create a fat binary for Mac x86_64 and Apple Silicon

* Remove the hint about the macOS SDK needed. It's no longer needed.

Author: michaelherger

COMPILING.md

@@ -180,6 +180,29 @@ Or to use rustls-tls with ALSA:
 cargo build --no-default-features --features "rustls-tls alsa-backend with-libmdns"
 ```
 
+### Compiling on Apple Silicon (M1+) for Apple x86_64
+
+Install the additional `x86_64-apple-darwin` target using rustup:
+
+```bash
+rustup target install x86_64-apple-darwin
+```
+
+Then run the build with the additional target parameter:
+
+```bash
+cargo build --target=x86_64-apple-darwin --release
+```
+
+You can then use the `lipo` tool to create a single fat (universal) binary for both platforms:
+
+```bash
+lipo -create \
+    -arch x86_64 target/x86_64-apple-darwin/release/librespot \
+    -arch arm64 target/aarch64-apple-darwin/release/librespot \
+    -output librespot
+```
+
 ### Running
 
 Assuming you just compiled a ```debug``` build, you can run librespot with the following command: