docs: Update sample-creator skill with agent topology graph rule

Co-authored-by: Shangjie Chen <deanchen@google.com>
PiperOrigin-RevId: 940581421

Author: DeanChensj

.agents/skills/adk-sample-creator/SKILL.md

@@ -89,7 +89,7 @@ Each sample should have a `README.md` with the following structure:
 
 - **Overview**: What the sample does.
 - **Sample Inputs**: Examples of inputs to test with. Each prompt must be wrapped in backticks. If a prompt has an explanation, always add a blank line between the prompt and the explanation, and indent the explanation by two spaces.
-- **Graph**: Visualization of the graph flow (Mermaid recommended for workflows).
+- **Graph**: Visualization of the graph flow (Mermaid recommended). For Workflow root agents, visualize the graph flow of nodes. For LlmAgent root agents that orchestrate tools or sub-agents, visualize the topology of the agent and its tools/sub-agents instead of internal workflow nodes.
 - **How To**: Explanation of key techniques used (e.g., `ctx.run_node`).
 - **Related Guides**: Links to relevant developer guides in `docs/guides/` that explain the concepts or classes used.
 
@@ -112,11 +112,18 @@ Brief description.
 
 ## Graph
 
+For Workflow root agents:
 ```mermaid
 graph TD
     START --> MyNode
 ```
 
+For LlmAgent root agents:
+```mermaid
+graph TD
+    MyAgent[my_agent] -->|calls| MyTool(my_tool)
+```
+
 ## How To
 
 Explain the details.