update context section in docs

Author: alexeyraspopov

docs/Details.md

@@ -43,3 +43,15 @@ Worth mentioning, `for..await` also can be used for producing content over time.
         yield <EventInfo event={event} />;
     }
 
+## Using context
+
+React Context is [accessible](https://facebook.github.io/react/docs/context.html#referencing-context-in-stateless-functional-components) in the same way as for stateless functional components:
+
+   async function* SomeCoroutine(props, context) {
+     for await (const message of context.dispatcher)
+       yield <SomeContent message={message} {...props} >;
+   }
+
+   SomeCoroutine.contextTypes = {
+     dispatcher: () => null
+   };