Update CONTRIBUTING.md

Co-authored-by: Janice <janiceilene@github.com>

CONTRIBUTING.md

@@ -38,7 +38,7 @@ Fork using the command line:
 ### Make your update:
 Make your changes to the file(s) you'd like to update. Here are some tips and tricks for [using the docs codebase](#working-in-the-githubdocs-repository).
   - Are you making changes to the application code? You'll need **Node.js v14** to run the site locally. See [contributing/development.md](contributing/development.md).
-  - Are you contributing to markdown? We use [GitHub Markdown](https://guides.github.com/features/mastering-markdown/).
+  - Are you contributing to markdown? We use [GitHub Markdown](contributing/content-markup-reference).
 
 ### Open a pull request
 When you're done making changes and you'd like to propose them for review, use the [pull request template](#pull-request-template) to open your PR (pull request).