update link to postcss-nesting (#142)

`postcss-nesting` was moved to https:/csstools/postcss-plugins/tree/main/plugins/postcss-nesting

README.md

@@ -81,7 +81,7 @@ Alternatives:
 [`postcss-current-selector`]: https:/komlev/postcss-current-selector
 [`postcss-nested-ancestors`]: https:/toomuchdesign/postcss-nested-ancestors
 [`postcss-nested-props`]: https:/jedmao/postcss-nested-props
-[`postcss-nesting`]: https:/jonathantneal/postcss-nesting
+[`postcss-nesting`]: https:/csstools/postcss-plugins/tree/main/plugins/postcss-nesting
 [CSSWG draft]: https://drafts.csswg.org/css-nesting-1/
 [PostCSS]: https:/postcss/postcss