Add a link to the DuckDuckHack Docs (#3381)

It took me a about an hour of trial-and-error before I found a link to the _DuckDuckHack Docs_ book inside the template module. I think it would be way more useful if this link was nearer the top of the README.

README.md

@@ -8,6 +8,7 @@ We're a community of open source developers from around the world, contributing
 - [**Create new Spice Instant Answers, and improve existing ones**](https://duckduckhack.com/issues)
     - **Note**: Spices are written in Perl (back-end) and JavaScript (front-end). They can also typically use CSS, and [Handlebars](http://handlebarsjs.com) Templates.
 - [**Visit DuckDuckHack**](https://duckduckhack.com/#get-help) to learn more about how you can help!
+- [**Read the DuckDuckHack Docs**](https://docs.duckduckhack.com/) to learn how to set up a development environment and start contributing!
 
 
 ### What are Spice Instant Answers?