Add language switcher on homepage (similar to gcloud-ruby)

From http://googlecloudplatform.github.io/gcloud-ruby/:

![gcloud-ruby-landing](https://cloud.githubusercontent.com/assets/112928/7541041/312d8146-f580-11e4-88c0-a18fbf78cc87.png)
