make twitter handle a link

Author: Gene Connolly

README.md

@@ -265,4 +265,4 @@ Achieving widespread support will require:
 _Immutable Web Apps_ was developed based on the research and experiences building web applications at [Meltwater](https://www.meltwater.com/). Learn more about the things we are doing at our engineering blog: [underthehood.meltwater.com](https://underthehood.meltwater.com/).
 
 [email protected]
-@immutablewebapp
+[@immutablewebapp](https://twitter.com/ImmutableWebApp)