docs: added more description about connecting UI with right mode. (#7119

)

docs/guide/ui.md

@@ -18,6 +18,10 @@ vitest --ui
 
 Then you can visit the Vitest UI at <a href="http://localhost:51204/__vitest__/">`http://localhost:51204/__vitest__/`</a>
 
+::: warning
+The UI is interactive and requires a running Vite server, so make sure to run Vitest in `watch` mode (the default). Alternatively, you can generate a static HTML report that looks identical to the Vitest UI by specifying `html` in config's `reporters` option.
+:::
+
 <img alt="Vitest UI" img-light src="/ui-1-light.png">
 <img alt="Vitest UI" img-dark src="/ui-1-dark.png">