Reference Windshaft's notes on Installing Mapnik

README.md

@@ -20,7 +20,7 @@ Requirements
    - npm >=1.2.1 <2.0.0
    - PostgreSQL >8.3.x, PostGIS >1.5.x
    - Redis >2.4.0 (http://www.redis.io)
-   - Mapnik 2.0.1, 2.0.2, 2.1.0, 2.2.0, 2.3.0. See Installing Mapnik.
+   - Mapnik 2.0.1, 2.0.2, 2.1.0, 2.2.0, 2.3.0. See [Installing Mapnik](https://github.com/CartoDB/Windshaft#installing-mapnik).
    - Windshaft: check [Windshaft dependencies and installation notes](https://github.com/CartoDB/Windshaft#dependencies)
    - libcairo2-dev, libpango1.0-dev, libjpeg8-dev and libgif-dev for server side canvas support