fix: Add example gif to readme

Author: aaronccasanova

README.md

@@ -1,2 +1,13 @@
+# Prettier Plugin CSS Grid
 
+An opinionated CSS Grid formatter.
 
+## Usage
+
+```sh
+npm i -D prettier-plugin-css-grid
+```
+
+> Note: Prettier will automatically detect this plugin and apply it to your code.
+
+![prettier-plugin-css-grid example](assets/prettier-plugin-css-grid.gif)