Updated readme

README.md

@@ -4,6 +4,13 @@ Simple, mobile-friendly dropdown menus.
 [Download Drop](https://github.com/cferdinandi/drop/archive/master.zip) / [View the demo](http://cferdinandi.github.io/drop/)
 
 
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+### Want to learn how to write your own vanilla JS plugins? Check out ["The Vanilla JS Guidebook"](https://gomakethings.com/vanilla-js-guidebook/) and level-up as a web developer. 🚀
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+<hr>
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 ## Getting Started