docs: add basic usage demo

Author: ghiscoding

README.md

@@ -32,6 +32,42 @@ The [Live demo](https://ghiscoding.github.io/multiple-select-vanilla/) website i
 npm install multiple-select-vanilla
 ```
 
+## Basic Usage
+
+#### 1. From a native `<select>`
+
+```html
+<select class="multiple-select full-width" data-test="select1">
+  <option value="1">First</option>
+  <option value="2">Second</option>
+  <option value="3">Third</option>
+  <option value="4">Fourth</option>
+</select>
+```
+
+and then initialize ms-select
+
+```ts
+import { multipleSelect } from 'multiple-select-vanilla';
+
+const ms = multipleSelect('.multiple-select');
+```
+
+##### 2. From data
+
+```ts
+import { multipleSelect } from 'multiple-select-vanilla';
+
+const ms = multipleSelect('.multiple-select', {
+  data: [
+    { text: 'First', value: 1 },
+    { text: 'Second', value: 2 },
+    { text: 'Third', value: 3 },
+    { text: 'Fourth', value: 4 },
+  ]
+});
+```
+
 ## Changelog
 
 [CHANGELOG](https://github.com/ghiscoding/multiple-select-vanilla/blob/main/packages/multiple-select-vanilla/CHANGELOG.md)