add screenshot

README.md

@@ -4,7 +4,7 @@ Crisp
 Crisp is one of Lisp dialect which is based on [mal](https://github.com/kanaka/mal) and implemented with [Crystal](https://github.com/manastech/crystal).
 This project is a toy box for my dynamic language ideas.
 
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+![screenshot](https://raw.githubusercontent.com/rhysd/screenshots/master/Crisp/crisp.gif)
 
 ## So Many Tasks