chore: add Readme

Author: Eazash

README.md

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+# Optimize Tailwindcss V3 selectors for `space-*` and `divide-*` classes
+
+> PostCSS plugin that optimizes the selectors & corresponding attributes for Tailwind CSS v3's `.space-*` and `.divide-*` utility classes
+
+For Use TailwindCSS V3
+> [!IMPORTANT] This plugin is intended for use with Tailwind CSS v3 as the problem this plugin solves is [already solved in v4](https://github.com/tailwindlabs/tailwindcss/pull/13459)
+
+## Why?
+
+In tailwindcss v3, the selector used for [`space-*`](https://v3.tailwindcss.com/docs/space) and [`divide-*`](https://v3.tailwindcss.com/docs/divide-width) utility classes was a relatively complex and slow selector used to accommodate hidden elements.
+
+```css
+/* before.css */
+.space-x-1 > :not([hidden]) ~ :not([hidden]) {
+  --tw-space-x-reverse: 0;
+  margin-right: calc(0.25rem * var(--tw-space-x-reverse));
+  margin-left: calc(0.25rem * calc(1 - var(--tw-space-x-reverse)));
+}
+```
+
+This slow selector can result in slow element render delays which then degrade page performance and FCP metrics for a page. TailwindCss v4 introduced a significantly faster selector that doesn't accommodate for hidden elements. 
+```css
+/* after.css */
+.space-x-1 > :not(:last-child) {
+  --tw-space-x-reverse: 0;
+  margin-right: calc(0.25rem * calc(1 - var(--tw-space-x-reverse)));
+  margin-left: calc(0.25rem * var(--tw-space-x-reverse));
+}
+```
+
+This Plugin ports these changes to v3. It also allows for using a v3 compatible selector that doesn't change the attributes
+```css
+/* when using `useV3CompatibleSelector: true` */
+/* after.css */
+.space-x-1 > * + * {
+  --tw-space-x-reverse: 0;
+  margin-right: calc(0.25rem * var(--tw-space-x-reverse));
+  margin-left: calc(0.25rem * calc(1 - var(--tw-space-x-reverse)));
+}
+```
+
+Important References
+- https://github.com/tailwindlabs/tailwindcss/discussions/13445#discussioncomment-9015050
+- https://github.com/tailwindlabs/tailwindcss/pull/13459
+- https://github.com/tailwindlabs/tailwindcss/issues/15162