Added a diagram

scraps/idea--persistent-chat-client

@@ -19,3 +19,6 @@ content: |
   It could also send the last dozen (or so) messages send and
   received to the client, so that switching client in
   mid-conversation will still keep the user in the loop.
+related:
+  - name: idea--persistent-chat-client-diagram
+    why: a more visual explanation