Update README.md (#287)

Added new marketing newsletter -- Geekout Newsletter

Author: awerb

README.md

@@ -455,6 +455,7 @@ Thanks to all [contributors](https://github.com/zudochkin/awesome-newsletters/gr
 - [Zero to Marketing](https://zerotomarketing.com/). A weekly email with 5-minute case study with actionable tips.
 - [The Content Odyssey](https://newsletter.mktodyssey.com/). Biweekly tried-and-tested content growth experiments.
 - [The Marketing Newsletter](http://themarketingnewsletter.org) - Ideas to help marketers and creators grow faster and work smarter
+- [Geekout Newsletter](https://geekout.mattnavarra.com/) - latest social media platform news, tips, tools, and new features
 
 ## Business/Finance