Added script to build a macOS bundle

build_mac.sh

@@ -0,0 +1,29 @@
+#!/bin/sh
+
+set -e
+
+rm -rf target/release/bundle/osx/Postsack.app
+
+# Build for x86 and ARM
+cargo build --release --target=aarch64-apple-darwin
+cargo build --release --target=x86_64-apple-darwin
+
+# Combine into a fat binary
+
+lipo -create target/aarch64-apple-darwin/release/postsack target/x86_64-apple-darwin/release/postsack -output postsack
+
+# Perform Cargo bundle to create a macOS Bundle
+
+cargo bundle --release
+
+# Override bundle binary with the fat one
+# Also: We want to have `Postsack` capitalized on macOS, so we rename
+
+rm target/release/bundle/osx/Postsack.app/Contents/MacOS/postsack
+
+mv ./postsack target/release/bundle/osx/Postsack.app/Contents/MacOS/
+
+# Tell the Info.plist or binary is capitalized
+
+/usr/libexec/PlistBuddy -c "Set :CFBundleExecutable Postsack" "target/release/bundle/osx/Postsack.app/Contents/Info.plist"
+