Merge nextjs-tailwind-mdx app template into examples

[rufuspollock]

Examples are a set of app templates (usually built on nextjs) and rather than have https://github.com/datopian/nextjs-tailwind-mdx separate makes sense to have it here (even if not using portal.js components out of the box).

Acceptance

• [x] https://github.com/datopian/nextjs-tailwind-mdx moved into examples/nextjs-tailwind-mdx
  • [x] Two issues moved here (with tweaks to titles)?
  • [x] Revise README with new install instructions
• [ ] Setup build in vercel or cloudflare (and add link to it to README?)
• [ ] nextjs-tailwind-mdx repo deleted (?)

Tasks

Same as acceptance?