docs(www): mention to add suppressHydrationWarning in the dark mode d…

…ocs for next

User have repeatedly run into hydration errors because they don't read the next-themes readme and don't pay attention to the shadcn/ui docs and miss that the `suppressHydrationWarning` prop must be added.

This commit mentions this explicitly and highlights the line in the snippet (as well as fixing the previously wrong highlighting).

apps/www/content/docs/dark-mode/next.mdx

@@ -33,9 +33,9 @@ export function ThemeProvider({
 
 ### Wrap your root layout
 
-Add the `ThemeProvider` to your root layout.
+Add the `ThemeProvider` to your root layout and add the `suppressHydrationWarning` prop to the `html` tag.
 
-```tsx {1,9-11} title="app/layout.tsx"
+```tsx {1,6,9-14,16} title="app/layout.tsx"
 import { ThemeProvider } from "@/components/theme-provider"
 
 export default function RootLayout({ children }: RootLayoutProps) {