Merge pull request ember-learn#695 from ember-learn/update-contributing-guide

Update CONTRIBUTING.md to point to the new infrastructure

Author: mansona

CONTRIBUTING.md

@@ -6,7 +6,7 @@ The Ember Guides are maintained and updated by an all-volunteer group of Ember c
 * _Contributing requested content_: We try to make it easy for people to contribute to the Guides by tagging issues with [help wanted](https://github.com/ember-learn/guides-source/issues?q=is%3Aopen+is%3Aissue+label%3A%22help+wanted%22) when appropriate. The best way to get started contributing content is to pick up one of these issues.
 Add a comment to let the maintainers know that you're interested, and post any questions you may have.
 * _Contributing unsolicited content_: If you'd like to contribute content that you think is missing, please start by checking the issues page. There may already be a plan to add this content! If not, open an issue yourself so that you can get feedback before you start writing. Our core contributors may ask you to start off by writing a blog post on your topic instead of or before opening a pull request on the Guides. This helps us keep the Guides consistent and streamlined.
-* _Writing infrastructure code_: You can also help out with the Guides by improving the code for the app that is used to build the content. Issues related to writing infrastructure code and layout should be made on the [guides-app](https://github.com/ember-learn/guides-app) repository.
+* _Writing infrastructure code_: You can also help out with the Guides by improving the code for the app that is used to build the content. The guides are powered by [Guidemaker](https://github.com/empress/guidemaker) and the styles and templates are provided by the [Guidemaker Ember Template](https://github.com/ember-learn/guidemaker-ember-template). If you have a specific issue that you are trying to fix and you're not sure which repo to work on then it is worth opening an issue on this repo and we can help to point you in the right direction. 
 
 Please note that no attempt is made to update content for older versions of the Guides. Except for broken links, they are considered static and immutable, as it is too difficult to maintain content for every version ever released. Issues will only be fixed for future releases.