docs: Add linking advice section
Add a new "Linking advice" section to the documentation requirements
document.
Fixes:
* [Introduction](#introduction)
* [General requirements](#general-requirements)
+* [Linking advice](#linking-advice)
* [Notes](#notes)
* [Warnings and other admonitions](#warnings-and-other-admonitions)
* [Files and command names](#files-and-command-names)
@@ -20,6 +21,18 @@ All documents must:
- Include a TOC (table of contents) at the top of the document with links to
all heading sections.
+# Linking advice
+
+Linking between documents is strongly encouraged to help users and developers
+navigate the material more easily. Linking also avoids repetition - if a
+document needs to refer to a concept already well described in another section
+or document, do not repeat it, link to it
+(the [DRY](https://en.wikipedia.org/wiki/Don%27t_repeat_yourself) principle).
+
+Another advantage of this approach is that changes only need to be applied in
+one place: where the concept is defined (not the potentially many places where
+the concept is referred to using a link).
+
# Notes
Important information that is not part of the main document flow should be
