docs: add icon documentation

Author: mrholek

packages/docs/content/4.0/api/CIcon.api.mdx

@@ -0,0 +1,19 @@
+
+```jsx
+import { CIcon } from '@coreui/react'
+// or
+import CIcon from '@coreui/react/src/components/icon/CIcon'
+```
+
+| Property | Description | Type | Default |
+| --- | --- | --- | --- |
+| **className** | A string of all className you want applied to the component. | `string` | - |
+| **content** | Use `icon={...}` instead of<br/>@deprecated since version 3.0 | `string` \| `string[]` | - |
+| **customClassName** | Use for replacing default CIcon component classes. Prop is overriding the 'size' prop. | `string` \| `object` \| `string[]` | - |
+| **height** | The height attribute defines the vertical length of an icon. | `number` | - |
+| **icon** | Name of the icon placed in React object or SVG content. | `string` \| `string[]` | - |
+| **name** | Use `icon="..."` instead of<br/>@deprecated since version 3.0 | `string` | - |
+| **size** | Size of the icon. Available sizes: 'sm', 'lg', 'xl', 'xxl', '3xl...9xl', 'custom', 'custom-size'. | `'custom-size'` \| `'sm'` \| `'lg'` \| `'xl'` \| `'xxl'` \| `'3xl'` \| `'4xl'` \| `'5xl'` \| `'6xl'` \| `'7xl'` \| `'8xl'` \| `'9xl'` | - |
+| **title** | Title tag content. | `string` | - |
+| **use** | If defined component will be rendered using 'use' tag. | `string` | - |
+| **width** | The width attribute defines the horizontal length of an icon. | `number` | - |