Fix link

README.rst

@@ -16,7 +16,7 @@ Performance
 -----------
 picows is implemented in Cython and provides unparalleled performance compared to other popular WebSocket libraries.
 
-.. image:: https://raw.githubusercontent.com/tarasko/picows/master/docs/picows_benchmark.png
+.. image:: https://raw.githubusercontent.com/tarasko/picows/master/docs/source/_static/picows_benchmark.png
   :target: https://github.com/tarasko/picows/blob/master/docs/source/_static/picows_benchmark.png?raw=true
 
 The above chart shows the performance of echo clients communicating with a server through a loopback interface using popular Python libraries.