Added html version of The Swift Programming Language

free-programming-books.md

@@ -1833,6 +1833,7 @@ See also [TeX](#tex)
 
 ### Swift
 * [The Swift Programming Language](https://itunes.apple.com/us/book/swift-programming-language/id881256329?mt=11) (iBook)
+* [The Swift Programming Language](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/index.html) (HTML)
 * [Using Swift with Cocoa and Objective-C](https://itunes.apple.com/us/book/using-swift-cocoa-objective/id888894773?mt=11) (iBook)
 * [Learn Swift](http://www.swift-tutorial.io/learn-swift)