add gem option to readme

.travis.yml

@@ -2,9 +2,11 @@ language: ruby
 bundler_args: --without debug
 script: bundle exec rake test_with_coveralls
 rvm:
+  - ruby-head
   - 2.1.0
   - 2.0.0
   - 1.9.3
+  - rbx-2
 notifications:
   email:
     recipients:

README.md

@@ -28,6 +28,10 @@ to a file in your plugin directory (e.g., to `_plugins/ext.rb`):
 
     require 'jekyll/scholar'
 
+Alternatively, add `jekyll-scholr` to your `gem` array in you configuration:
+
+    gem: ['jekyll-scholar']
+
 In your configuration you can now adjust the Jekyll-Scholar settings. The
 default configuration is as follows: