Add link to docs repo and renamed page

doc/development/documentation/site_architecture/index.md

@@ -2,11 +2,18 @@
 description: "Learn how GitLab's documentation website is architectured."
 ---
 
-# Docs site architecture
+# Documentation site architecture
 
 Learn how we build and architecture [`gitlab-docs`](https://gitlab.com/gitlab-com/gitlab-docs)
 and deploy it to <https://docs.gitlab.com>.
 
+## Repository
+
+While the source of the documentation content is stored in GitLab's respective product
+repositories, the source that is used to build the documentation site _from that content_
+is located at https://gitlab.com/gitlab-com/gitlab-docs. See the README there for
+detailed information.
+
 ## Assets
 
 To provide an optimized site structure, design, and a search-engine friendly