Add missing elli link

yurrriq · yurrriq · commit 3ef4d35d6e50 · 2016-04-18T20:46:38.000-05:00
diff --git a/README.md b/README.md
@@ -6,6 +6,7 @@ An [elli][] middleware to add the following header to all responses:
 X-Powered-By: LFE
 ```
 
+[elli]: https://github.com/knutin/elli
 
 ## Usage:
 
