Update README.md

bootstrap-pull-request/README.md

@@ -1,7 +1,26 @@
 # bootstrap-pull-request [![bootstrap-pull-request](https://github.com/quipper/monorepo-deploy-actions/actions/workflows/bootstrap-pull-request.yaml/badge.svg)](https://github.com/quipper/monorepo-deploy-actions/actions/workflows/bootstrap-pull-request.yaml)
 
 This is an action to bootstrap the pull request namespace.
-It should be called when a pull request is created or updated.
+When a pull request is created or updated, this action copies the service manifests from the prebuilt branch.
+
+```mermaid
+graph LR
+  subgraph Source repository
+    SourceNamespaceManifest[Namespace manifest]
+  end
+  subgraph Destination repository
+    subgraph Prebuilt branch
+      PrebuiltServiceManifest[Service manifest]
+    end
+    subgraph Namespace branch
+      ApplicationManifest[Application manifest]
+      ServiceManifest[Service manifest]
+      NamespaceManifest[Namespace manifest]
+    end
+  end
+  PrebuiltServiceManifest --Copy--> ServiceManifest
+  SourceNamespaceManifest --Copy--> NamespaceManifest
+```
 
 ## Getting Started