move documentation/ to docs/

docs/.vitepress/theme/index.ts

@@ -0,0 +1,17 @@
+// https://vitepress.dev/guide/custom-theme
+import { h } from 'vue'
+import type { Theme } from 'vitepress'
+import DefaultTheme from 'vitepress/theme'
+import './style.css'
+
+export default {
+  extends: DefaultTheme,
+  Layout: () => {
+    return h(DefaultTheme.Layout, null, {
+      // https://vitepress.dev/guide/extending-default-theme#layout-slots
+    })
+  },
+  enhanceApp({ app, router, siteData }) {
+    // ...
+  }
+} satisfies Theme