Add default MiniMax character reference image

optimized/image-to-video/minimax-h3-r2v-master/prompt-guide.md

@@ -6,6 +6,9 @@ Short prompt-authoring companion for the maintained `MiniMax H3` `r2v`
 master. This keeps the prompt shape close to MiniMax's official H3 docs while
 matching the local ComfyUI workflow that Chris is actually using.
 
+Bundled default Subject 1 character reference image:
+`references/default-character-reference.jpg`
+
 ## Official MiniMax doc takeaways
 
 Based on:
@@ -36,6 +39,9 @@ Key points worth preserving:
 
 - Treat `<Picture 1>` as the environment / master-scene reference when an
   environment reference is used.
+- Treat `references/default-character-reference.jpg` as the default file to
+  load into `<Picture 2>` when you need a starter Subject 1 full-body
+  reference and have not chosen a different one yet.
 - Group all images belonging to the same character explicitly.
 - State what each reference controls and what it must not control.
 - Ignore the backgrounds of character references unless a reference is