docs: add pure usage to website

Author: DylanVann

packages/docs/usage.md

@@ -114,3 +114,18 @@ mode.update((mode) => (mode === 'light' ? 'dark' : 'light'))
       be updated by the user in their system settings.
     - We do listen for changes to the OS color mode.
     - `subscribe(listener: (mode: ColorMode) => void): () => void`
+
+## Pure Usage
+
+If for some reason you don't want PDM to automatically initialize itself and add itself on `window.__pdm__` you can use the pure version:
+
+```js
+import { createPerfectDarkMode } from 'perfect-dark-mode'
+
+const pdm = createPerfectDarkMode()
+```
+
+This version comes in a couple module formats:
+
+- `dist/pure.esm.js`
+- `dist/pure.cjs.js`