add learn.adicu.com to sidebar

closes #85 

initial: ![screen shot 2013-09-22 at 11 52 19 pm](https://f.cloud.github.com/assets/2801090/1189147/97ee1c06-2403-11e3-8b84-3b391864fe85.png)

changed: ![screen shot 2013-09-22 at 11 49 25 pm](https://f.cloud.github.com/assets/2801090/1189146/63a25520-2403-11e3-8adc-8c0dc86fc4b0.png)