docs: Add missing link to outreach TOC.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

docs/index.md

@@ -33,7 +33,8 @@ Contents:
 - {ref}`Code testing <code-testing>`
 - {ref}`Subsystem documentation <subsystem-documentation>`
 - {ref}`Writing documentation <writing-documentation>`
-- {ref}`Translating <translating>`
+- {ref}`Translating Zulip <translating>`
+- {ref}`Outreach programs <outreach>`
 
 (overview)=