Add autoprefixer known limitation to readme

When I first tried to use the new compiler, I bumped into this error:
`Maximum call stack size exceeded`
Thanks to #29, I noticed that I must use the latest version of the `autoprefixer`, which indeed fixed this issue.
Unfortunately, it can't be found anywhere in the docs.

Author: idoshamun

README.md

@@ -118,6 +118,7 @@ There are a few items still on our todo list though that we are actively working
 - The `important` option does not yet support selectors (like `#app`).
 - Advanced PurgeCSS options like `safelist` aren't supported yet since we aren't actually using PurgeCSS. We'll add a way to safelist classes for sure though. For now, a `safelist.txt` file somewhere in your project with all the classes you want to safelist will work fine.
 - You can only `@apply` classes that are part of core, generated by plugins, or defined within a `@layer` rule. You can't `@apply` arbitrary CSS classes that aren't defined within a `@layer` rule.
+- Requires updating `autoprefixer` to the latest version using (`npm install -D autoprefixer@latest`). Does not support the latest `postcss-preset-env` due to `autoprefixer` version.
 
 If you run into any other issues or find any bugs, please [open an issue](https://github.com/tailwindlabs/tailwindcss-jit/issues/new) so we can fix it.