E09: Product documentation backlog (#101)

delivery_backlog/README.md

@@ -2,13 +2,14 @@
 
 This backlog decomposes the phases in
 [`INTEGRATED_PIPELINE_CONCEPT.md`](../INTEGRATED_PIPELINE_CONCEPT.md) into seven
-epics and small, independently verifiable user stories, plus one delivery-format
-epic (E08) that packages the released application as a deployable container.
+epics and small, independently verifiable user stories, plus two delivery-format
+epics: E08 packages the released application as a deployable container, and E09
+documents it for the people who install, operate, and use it.
 
 ## Numbering and file naming
 
-- Epics: `E01` through `E07`, matching concept Phases A through G; `E08` has no
-  concept phase and must not change product scope.
+- Epics: `E01` through `E07`, matching concept Phases A through G; `E08` and `E09`
+  have no concept phase and must not change product scope.
 - Stories: `US<epic>-<sequence>`, for example `US03-02`.
 - Epic files: `E01-<slug>.md`.
 - Story files: `stories/US01-01-<slug>.md`.
@@ -39,6 +40,7 @@ epic (E08) that packages the released application as a deployable container.
 6. [E06 — Archive lifecycle](E06-archive-lifecycle.md)
 7. [E07 — Hardening and release](E07-hardening-release.md)
 8. [E08 — Container deployment](E08-container-deployment.md)
+9. [E09 — Product documentation](E09-documentation.md)
 
 ## Shared definition of done