Update README.md

Author: thomashoneyman

README.md

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 [PureScript](https://github.com/purescript) is a delightful purely-functional language that offers powerful, pragmatic tools to manage complexity and help you design, build, and refactor reliable apps of any size. This repository demonstrates the principles I apply at work every day in more than 2,000 lines of thoroughly commented code and has an accompanying long-form [guide to building real-world Halogen applications](https://thomashoneyman.com/guides/real-world-halogen).
 
+> Using Halogen 5? See the [fully-functioning branch of RealWorld for Halogen 5](https://github.com/thomashoneyman/purescript-halogen-realworld/tree/halogen-5)
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 I’m a senior software engineer at [Awake Security](https://github.com/awakesecurity) (and previously at [CitizenNet](https://citizennet.com)). Both companies have large production PureScript applications that have remained reliable, understandable, and maintainable as they scale. I’m convinced PureScript is the best language available today for most single-page applications.
 
 This repository follows the [RealWorld](https://github.com/gothinkster/realworld) spec to implement a Medium clone called Conduit using [Halogen](https://github.com/slamdata/purescript-halogen). It’s large enough to demonstrate real world examples (CRUD, state management, scalable architecture, type classes, components, etc.) but not so large as to be overwhelming.