Add Package.swift (#39)

* Add Package.swift for LLM and MNIST
* Make ModelType properties public
* Make ModelType method createModel public
* Add installation instructions to readme

.gitignore

@@ -37,14 +37,14 @@ playground.xcworkspace
 # Swift Package Manager
 #
 # Add this line if you want to avoid checking in source code from Swift Package Manager dependencies.
-# Packages/
-# Package.pins
-# Package.resolved
+Packages/
+Package.pins
+Package.resolved
 # *.xcodeproj
 #
 # Xcode automatically generates this directory with a .xcworkspacedata file and xcuserdata
 # hence it is not needed unless you have added a package configuration file to your project
-# .swiftpm
+.swiftpm
 
 .build/
 
@@ -88,3 +88,7 @@ fastlane/test_output
 # https://github.com/johnno1962/injectionforxcode
 
 iOSInjectionProject/
+
+# OS
+.DS_Store
+