update README.md

Author: romainmenke

packages/base-cli/README.md

@@ -1,3 +1,20 @@
 # PostCSS Base Plugin [<img src="https://postcss.github.io/postcss/logo.svg" alt="PostCSS Logo" width="90" height="90" align="right">][postcss]
 
-<!-- TODO -->
+```ts
+import plugin from '@csstools/postcss-base-plugin';
+import { cli, helpTextLogger } from '@csstools/base-cli';
+
+cli(
+	plugin,
+	['color', 'another_option'],
+	helpTextLogger(
+		'postcss-base-plugin-cli',
+		'Base Plugin',
+		'An example plugin CLI',
+		{
+			color: 'A CSS color',
+			another_option: true,
+		},
+	),
+);
+```