Add layout guidelines to README

Add the expectations for the utilisation of the various existing sections
to the website README.md to help guide contributors.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

README.md

@@ -8,6 +8,29 @@ is served from gitlab pages.
 
 ---
 
+## Document layout
+
+When adding documents to the Apertis Website, please adhere to the following
+layout guidelines:
+
+- Policies:
+  - Documenting procedures and rules
+  - Minimal requirements for project involvement
+- Concepts:
+  - Topics that have been researched and/or planned but which haven't yet been implemented
+- Architecture:
+  - Description of project infrastructure
+  - Details of technologies and software used by Apertis
+- Guides:
+  - Guidance on using specific software features
+  - Worked examples of expected project workflows
+- QA:
+  - Test reports
+  - Test procedures (realistically, a description of the testing performed and a pointer to qa.apertis.org)
+- Releases:
+  - Release notes
+  - Release schedules
+
 ## GitLab CI
 
 This project's static Pages are built by [GitLab CI][ci], following the steps