nef - integration with Carbon (#807)

* nef integration

* adding more details about `nef`

* link to how create an Xcode playground using nef

* Update README.md

* added link to carbon section in nef

README.md

@@ -97,6 +97,7 @@ Check out these projects our awesome community has created:
 - [CLI `carbon-now-cli`](https://github.com/mixn/carbon-now-cli) - Open a file in Carbon or download it directly using `carbon-now`, featuring an interactive mode, selective highlighting and more
 - [Carbonize](https://itunes.apple.com/us/app/carbonize/id1451177988) - A macOS wrapper with extended native features
 - [CodeExpander](https://codeexpander.com) - A smart GitHub gist client with the TextExpander features
+- [`nef`](https://github.com/bow-swift/nef#-exporting-carbon-code-snippets) - Export multiple Carbon code snippets from `Xcode Playground`.
 
 ##### Libraries