organise content by subject

doc/development/doc_styleguide.md

@@ -18,6 +18,10 @@ like `docs.gitlab.com/user/project/merge_requests.html`. With this pattern,
 you can immediately tell that you are navigating a user related documentation
 and is about the project and its merge requests.
 
+Do not create summaries of similar types of content (e.g. an index of all articles, videos, etc.),
+rather organise content by its subject (e.g. everything related to CI goes together)
+and cross-link between any related content.
+
 The table below shows what kind of documentation goes where.
 
 | Directory | What belongs here |