Create PR to add note about StrictMode causing double renders

[DavidCao22]

Spot to add note: https://github.com/reactjs/react.dev/blame/abe931a8cb3aee3e8b15ef7e187214789164162a/src/content/learn/describing-the-ui.md#L477

[DavidCao22]

Edit should probably something like this
https://github.com/reactjs/react.dev/blob/abe931a8cb3aee3e8b15ef7e187214789164162a/src/content/learn/passing-props-to-a-component.md?plain=1#L85

[DavidCao22]

Or just link to the existing node about StrictMode: https://react.dev/learn/keeping-components-pure#detecting-impure-calculations-with-strict-mode