Build script for self-contained Mac .app (#185)

* Add CMake settings to build universal binary and find SDL in app bundle

* Source frameworks from extern folder

* Add build script, info plist and big sur style icon

* Add example build workflow (app won't be signed)

* Use macOS 11 runner for better compatibility

* Use better name for the build script, move metadata to Platform/macOS/ folder

* Improve macOS build instructions

* Fix workflow syntax and use a more specific glob pattern too

* Add libs search paths to CMakeLists.txt instead of find files

* Use same /Libs folder as libs search path

* Make build-mac-app.sh not fail on repeated runs

* Make build-mac-app.sh executable

README.md

@@ -74,6 +74,10 @@ This project is available as Flatpak on [Flathub](https://flathub.org/apps/detai
 
 ### On macOS
 
+Install XCode (or at least Xcode Command Line Tools with `xcode-select --install`) and CMake.
+
+**Manual compilation:**
+
 * **Homebrew**: Install the `SDL2`, `SDL2_mixer` homebrew packages.
 * **MacPorts**: Install the `libSDL2`, `libSDL2_mixer` macports packages.
 
@@ -81,6 +85,12 @@ Compile with CMake. Ensure that `CMAKE_OSX_ARCHITECTURES` variable is set for ei
 
 Tested with: macOS Big Sur (Intel) with Xcode 13 & macOS Montery Beta (Apple Silicon) with Xcode 13.
 
+**Automated compilation:**
+
+Run the `build-mac-app.sh` script from the root of the repository. The app will be available in a DMG file named `SpaceCadetPinball-<version>-mac.dmg`.
+
+Tested with: macOS Ventura (Apple Silicon) with Xcode Command Line Tools 14 & macOS Big Sur on GitHub Runner (Intel) with XCode 13.
+
 ## Plans
 
 * ~~Decompile original game~~