Update _config.yml

Author: keveleigh

docs/_config.yml

@@ -9,6 +9,12 @@ url: https://mixedrealitytoolkit.github.io/MixedRealityToolkit-Unity/
 logo: "/images/MRTK_Logo_White.png"
 favicon_ico: "/images/IconMRTKLogo.png"
 
+plugins:
+  - jekyll-relative-links
+relative_links:
+  enabled: true
+  collections: true
+
 defaults:
   - scope:
       path: "" # an empty string here means all files in the project