Mention swift-2.3 branch in documentation

Author: jberkel

README.md

@@ -1,4 +1,4 @@
-# SQLite.swift 
+# SQLite.swift
 
 [![Build Status][Badge]][Travis] [![CocoaPods Version](https://cocoapod-badges.herokuapp.com/v/SQLite.swift/badge.png)](http://cocoadocs.org/docsets/SQLite.swift) [![Swift](https://img.shields.io/badge/swift-3-orange.svg?style=flat)](https://developer.apple.com/swift/) [![Platform](https://cocoapod-badges.herokuapp.com/p/SQLite.swift/badge.png)](http://cocoadocs.org/docsets/SQLite.swift) [![Carthage compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage) [![Join the chat at https://gitter.im/stephencelis/SQLite.swift](https://badges.gitter.im/stephencelis/SQLite.swift.svg)](https://gitter.im/stephencelis/SQLite.swift)
 
@@ -109,7 +109,9 @@ For a more comprehensive example, see [this article](http://masteringswift.blogs
 
 ## Installation
 
-> _Note:_ SQLite.swift requires Swift 3 (and [Xcode][] 8) or greater.
+> _Note:_ SQLite.swift requires Swift 3 (and [Xcode][] 8) or greater. If you absolutely
+> need compatibility with Swift 2.3 you can use the [swift-2.3][] branch or older
+> released versions. New development will happen exclusively on the master/Swift 3 branch.
 >
 > The following instructions apply to targets that support embedded
 > Swift frameworks. To use SQLite.swift in iOS 7 or an OS X command line
@@ -199,7 +201,7 @@ To install SQLite.swift as an Xcode sub-project:
  - Found a **bug** or have a **feature request**? [Open an issue][].
  - Want to **contribute**? [Submit a pull request][].
 
-[See the planning document]: /Documentation/Planning.md 
+[See the planning document]: /Documentation/Planning.md
 [Read the contributing guidelines]: ./CONTRIBUTING.md#contributing
 [Ask on Stack Overflow]: http://stackoverflow.com/questions/tagged/sqlite.swift
 [Open an issue]: https://github.com/stephencelis/SQLite.swift/issues/new
@@ -237,3 +239,4 @@ Looking for something else? Try another Swift wrapper (or [FMDB][]):
  - [SwiftSQLite](https://github.com/chrismsimpson/SwiftSQLite)
 
 [FMDB]: https://github.com/ccgus/fmdb
+[swift-2.3]: https://github.com/stephencelis/SQLite.swift/tree/swift-2.3