fix developer docs link (#28)

Author: mauerbac

README.md

@@ -16,7 +16,7 @@ pip install optimizely-sdk
 ```
 
 ###Using the SDK
-See the Optimizely server-side testing [developer documentation](http://developers.optimizely.com/server/reference/index) to learn how to set up your first custom project and use the SDK. **Please note that you must be a member of the private server-side testing beta to create custom projects and use this SDK.**
+See the Optimizely server-side testing [developer documentation](http://developers.optimizely.com/server/reference/index.html) to learn how to set up your first custom project and use the SDK. **Please note that you must be a member of the private server-side testing beta to create custom projects and use this SDK.**
 
 ##Development