Fix NextJS migration snippet (#5307)

Co-authored-by: Sarah Rainsberger <[email protected]>
Co-authored-by: Atharva Pise <[email protected]>

src/content/docs/en/guides/migrate-to-astro/from-nextjs.mdx

@@ -504,12 +504,14 @@ Here's how to recreate that in `src/pages/index.astro`, replacing `getStaticProp
 
     - The `<> </>` fragment is not required in Astro templating.
 
+    - `key` is a React attribute, and is not an attribute of `li` in Astro.
+
     ```astro title="src/pages/index.astro" "class" "</a>" "<a"
     ---
     ---
     <ul class="plain-list pokeList">
         {pokemons.map((pokemon) => (
-            <li class="pokemonListItem" key={pokemon.name}>
+            <li class="pokemonListItem">
                 <a class="pokemonContainer" href={`/pokemon/${pokemon.name}`}>
                     <p class="pokemonId">No. {pokemon.id}</p>
                     <img class="pokemonImage" src={`https://raw.githubusercontent.com/PokeAPI/sprites/master/sprites/pokemon/${pokemon.id}.png`} alt={`${pokemon.name} picture`}/>