Add new blog post

https://pspdfkit.com/blog/2019/how-to-extend-react-native-apis-for-windows/

Author: steipete

README.md

@@ -13,6 +13,7 @@ This wrapper requires a valid license of PSPDFKit. Licenses are per platform. Yo
   Native](https://pspdfkit.com/blog/2018/introducing-pspdfkit-windows/#react-native-for-windows-support) ([See Windows UWP](https://github.com/PSPDFKit/react-native#windows-uwp))
 - [How to Extend React Native APIs](https://pspdfkit.com/blog/2018/how-to-extend-react-native-api/)
 - [Advanced Techniques for React Native UI Components](https://pspdfkit.com/blog/2018/advanced-techniques-for-react-native-ui-components/)
+- [How to Extend React Native APIs for Windows](https://pspdfkit.com/blog/2019/how-to-extend-react-native-apis-for-windows/)
 
 #### PSPDFKit