Update smoke test command to confirm successful installation of mcp-agent (lastmile-ai#584)

Author: StreetLamb

docs/get-started/install.mdx

@@ -160,7 +160,7 @@ mcp-agent works with any MCP server. Install the ones you need:
 
   <Step title="Smoke test">
     ```bash
-    uv run python -c "import mcp_agent; print(mcp_agent.__version__)"
+    uv run python -c "import mcp_agent; print('mcp-agent installed successfully!')"
     ```
   </Step>
 </Steps>