Added link to the Flutter package for rendering Portable Text (#30)

* Added link to the Flutter package for rendering Portable Text

Added links and the supporting package

* Update README.md

Co-authored-by: Knut Melvær <knut.melvaer@gmail.com>

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Co-authored-by: Knut Melvær <knut.melvaer@gmail.com>

README.md

@@ -212,6 +212,7 @@ Examples of custom blocks:
 
 #### Dart/Flutter
 
+- [Flutter Widget for Portable Text](https://pub.dev/packages/flutter_sanity_portable_text): Supports the entire spec of Portable Text with an easy to use Widget. It also includes support for **custom** blocks, marks, gestures, styles in an extensible manner. Use this package in conjunction with the [Sanity Client](https://pub.dev/packages/sanity_client) package for deserializing Portable Text in documents from Sanity.
 - [flutter_portabletext](https://github.com/JobiJoba/flutter_portabletext)
 
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