docs(site): highlight augmenting existing ADO pipelines via stage generator (#909)

* docs(site): add section on augmenting existing ADO pipelines

Co-authored-by: jamesadevine <4742697+jamesadevine@users.noreply.github.com>

* docs(site): focus augment section on stage generator

Co-authored-by: jamesadevine <4742697+jamesadevine@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jamesadevine <4742697+jamesadevine@users.noreply.github.com>

Author: Copilot

site/src/content/docs/index.mdx

@@ -122,6 +122,23 @@ flowchart TD
 
 ---
 
+## Augment your existing pipelines
+
+Already have Azure DevOps pipelines you rely on? You don't have to start from scratch. Compile an agent with `target: stage` and ado-aw emits a reusable, stage-level template you can drop straight into an existing multi-stage pipeline -- no rewrites required.
+
+```yaml
+stages:
+  - stage: Build
+    jobs: ...
+  - template: agents/review.lock.yml   # the agentic workflow, slotted in
+    parameters:
+      dependsOn: Build
+```
+
+The same three-job security chain (Agent → Detection → SafeOutputs) runs as part of your current pipeline, so you can layer continuous AI onto the workflows you already trust. See [Target platforms](/ado-aw/reference/targets/) for details.
+
+---
+
 ## Get started in minutes
 
 <CardGrid>