Modify For New ERA Apple Silicon

.github/APPLE_SILICON_SUPPORT.md

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+# Apple Silicon Support
+
+MacDown now has full support for Apple Silicon (ARM64) Macs running macOS 11 Big Sur and later.
+
+## Architecture Support
+
+The project is built and tested on **two architectures**:
+
+- **Apple Silicon (ARM64)**: Built on macOS 14 (latest Apple Silicon runner)
+- **Intel (x86_64)**: Built on macOS 12 (Intel runner)
+
+## Build Configuration
+
+### Podfile
+The `Podfile` includes a `post_install` hook that ensures all CocoaPods dependencies support both architectures:
+
+```ruby
+post_install do |installer|
+  installer.pods_project.targets.each do |target|
+    target.build_configurations.each do |config|
+      config.build_settings['ARCHS'] = '$(ARCHS_STANDARD)'
+      config.build_settings['VALID_ARCHS'] = 'x86_64 arm64'
+    end
+  end
+end
+```
+
+### CI/CD Build Process
+
+Both `.github/workflows/build.yml` and `.github/workflows/release.yml` use a matrix strategy to build for both architectures:
+
+- Each architecture gets its own dedicated macOS runner
+- `ARCHS` flag is explicitly set during xcodebuild to target the specific architecture
+- Separate build products and artifacts are created for each architecture
+
+## Releases
+
+When you create a release (via `git tag v1.0.0`), the CI/CD pipeline automatically:
+
+1. Builds for both ARM64 and x86_64
+2. Creates separate DMG files for each architecture:
+   - `MacDown-v1.0.0-arm64.dmg` (Apple Silicon)
+   - `MacDown-v1.0.0-x86_64.dmg` (Intel)
+3. Publishes both DMGs to the GitHub release
+
+Users can download the version appropriate for their Mac:
+- **Apple Silicon Mac**: Use `arm64` version
+- **Intel Mac**: Use `x86_64` version
+
+## Local Development
+
+### Building for Apple Silicon (on Apple Silicon Mac)
+```bash
+xcodebuild -workspace MacDown.xcworkspace \
+  -scheme MacDown \
+  -configuration Release \
+  ARCHS=arm64 \
+  build
+```
+
+### Building for Intel (on Apple Silicon Mac with Rosetta)
+```bash
+xcodebuild -workspace MacDown.xcworkspace \
+  -scheme MacDown \
+  -configuration Release \
+  ARCHS=x86_64 \
+  build
+```
+
+### Building for Both (Universal Binary)
+```bash
+xcodebuild -workspace MacDown.xcworkspace \
+  -scheme MacDown \
+  -configuration Release \
+  ARCHS='arm64 x86_64' \
+  build
+```
+
+## CocoaPods Compatibility
+
+All CocoaPods dependencies used in MacDown support Apple Silicon:
+
+- handlebars-objc
+- hoedown
+- JJPluralForm
+- LibYAML
+- M13OrderedDictionary
+- MASPreferences
+- Sparkle
+- PAPreferences
+- GBCli (macdown-cmd target)
+
+If you need to add new dependencies, ensure they support ARM64 architecture before adding to the Podfile.
+
+## Testing
+
+Both architectures are tested in CI/CD:
+
+```bash
+# Tests run on both macOS 14 (Apple Silicon) and macOS 12 (Intel)
+xcodebuild -workspace MacDown.xcworkspace \
+  -scheme MacDown \
+  -configuration Debug \
+  test
+```
+
+## Troubleshooting
+
+### Pod Install Fails for ARM64
+
+If you encounter pod install issues on Apple Silicon, try:
+
+```bash
+# Clear pods and reinstall
+rm -rf Pods
+rm Podfile.lock
+pod install
+```
+
+### Build Fails with "Architecture Mismatch"
+
+Ensure you're using the correct `ARCHS` setting and that all dependencies are properly installed via CocoaPods.
+
+### Rosetta 2 Builds on Apple Silicon
+
+If building for x86_64 on Apple Silicon via Rosetta 2:
+
+```bash
+# Use arch command to run in x86_64 mode
+arch -x86_64 /usr/bin/ruby -I/usr/local/lib/ruby/gems/3.0.0 /usr/local/bin/pod install
+```
+
+## Future Improvements
+
+- Consider creating universal binaries (both arm64 + x86_64 in one DMG) for simplified distribution
+- Monitor minimum macOS deployment target for potential modernization
+- Keep CocoaPods dependencies updated for optimal ARM64 support