Adding Swiftype search and autocomplete

Following environment variables should be loaded in the app,
can be added to ``secret.rb`` file.

```
ENV['SWIFTYPE_API_KEY'] = "R9opsbyx4EvwopBYnzNx"
ENV['SWIFTYPE_ENGINE_SLUG'] = "rubygems"
ENV['SWIFTYPE_ENGINE_KEY'] = 'sZFvPEri_3KjkM2i-6V_'
```

Please contact us to setup a Swiftype account for rubygems.org.