[website] Add "React" to the /x page hero description

[danilo-leal]

• I have followed (at least) the PR section of the contributing guide.

Adding the "React" word to the /x page hero and SEO description. This is an iteration after one customer bought MUI X Pro thinking it was actually buying the Design Kits. We weren't mentioning that the /x page as about React components as well so maybe this helps to avoid this same confusion happening again.

Preview: https://deploy-preview-28830--material-ui.netlify.app/x/

[danilo-leal]

@oliviertassinari Following up on the email you forwarded! Let me know if you have any other ideas to help clearing the confusion around :) I think that adding to the hero and SEO might be enough, otherwise, it gets too repetitive.

[mui-pr-bot]

No bundle size changes

Generated by 🚫 dangerJS against 3d911dd

[oliviertassinari]

Looks great, I was thinking of the same change. I have a number of similar quick-wins pilling up in my todo-list 😁.

[danilo-leal]

@oliviertassinari Do you want to go all-in and have them addressed here? No prob with that!
If they're all copywriting-wise, the branch name still works, I'd only change the PR title 😅

[oliviertassinari]

I don't have the time now. I will look at it later, maybe this weekend.

[danilo-leal]

Alright! I'm merging this one so it enters this week's release. Feel free to hand me over the list of changes you have there though, I can walk through them if you're busy!