Add note to JIT post

Author: adamwathan

src/pages/just-in-time-the-next-generation-of-tailwind-css/index.mdx

@@ -17,6 +17,8 @@ export const meta = {
   `,
 }
 
+_**Update**: As of Tailwind CSS v2.1, the new Just-in-Time engine is included right in Tailwind CSS itself, so you don't need the `@tailwindcss/jit` package anymore. [Learn more in the documentation](https://tailwindcss.com/docs/just-in-time-mode)._
+
 One of the hardest constraints we've had to deal with as we've improved Tailwind CSS over the years is the generated file size in development. With enough customizations to your config file, the generated CSS can reach 10mb or more, and there's only so much CSS that build tools and even the browser itself will comfortably tolerate.
 
 For that reason, you've always had to be careful about expensive changes to your config file like adding too many extra breakpoints or enabling extra variants like `disabled` or `focus-visible`.