Add VitePress docs site with MoonBit highlighting

docs/.vitepress/theme/index.ts

@@ -0,0 +1,17 @@
+import DefaultTheme from 'vitepress/theme'
+import type { Theme } from 'vitepress'
+
+import ApiOverview from './components/ApiOverview.vue'
+import HomeDocHub from './components/HomeDocHub.vue'
+
+import './custom.css'
+
+const theme: Theme = {
+  extends: DefaultTheme,
+  enhanceApp({ app }) {
+    app.component('ApiOverview', ApiOverview)
+    app.component('HomeDocHub', HomeDocHub)
+  },
+}
+
+export default theme