Documentation improvements

- Link to classes as examples
- Link directly to `receive_test` example

Author: pbrisbin

README.md

@@ -103,11 +103,19 @@ The following are not fully implemented yet.
 To add a new integration, you'll need to create a new `Service` subclass. Please
 use existing services as an example:
 
-- Chat service examples: `hipchat`, `campfire`
-- Issue tracker examples: `github_issues`, `lighthouse`
+- Chat service examples: [hipchat][], [campfire][]
+- Issue tracker examples: [github_issues][], [lighthouse][]
+
+[hipchat]: /codeclimate/codeclimate-services/blob/master/lib/cc/services/hipchat.rb
+[campfire]: /codeclimate/codeclimate-services/blob/master/lib/cc/services/campfire.rb
+[github_issues]: /codeclimate/codeclimate-services/blob/master/lib/cc/services/github_issues.rb
+[lighthouse]: /codeclimate/codeclimate-services/blob/master/lib/cc/services/lighthouse.rb
 
 Ensure that your class implements `#receive_test`. It must handle any exceptions
 and always return a hash of `{ ok: true|false, message: "String (HTML ok)" }`.
+[Example][test_example].
+
+[test_example]: /codeclimate/codeclimate-services/blob/master/lib/cc/services/jira.rb#L31
 
 When you open your PR, please include an image for your service.
 [Example][service_avatar].