updated free iOS book (#7584)

* updated free iOS book

* removed blank line

* chore: add creators

* lint: alphabetize

Co-authored-by: Biswadeep Purkayastha <98874428+metabiswadeep@users.noreply.github.com>

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>
Co-authored-by: Biswadeep Purkayastha <98874428+metabiswadeep@users.noreply.github.com>

books/free-programming-books-langs.md

@@ -955,6 +955,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 ### iOS
 
 * [Cocoa Dev Central](http://cocoadevcentral.com)
+* [Develop in Swift Explorations](https://books.apple.com/in/book/develop-in-swift-explorations/id1581182728) - Apple Education (iBook)
 * [Essential iOS](https://www.programming-books.io/essential/ios/) - Krzysztof Kowalczyk, StackOverflow Contributors
 * [iOS Developer Notes for Professionals](https://goalkicker.com/iOSBook/) - Compiled from StackOverflow Documentation (PDF)
 * [iOS Succinctly, Syncfusion](https://www.syncfusion.com/resources/techportal/ebooks/ios) (PDF, Kindle) (email address *requested*, not required)