docs: add documentation for LLMs (llms.txt) (#189)

Thanks to https://github.com/okineadev/vitepress-plugin-llms

docs/.vitepress/theme/index.ts

@@ -1,5 +1,6 @@
 import type { Theme } from 'vitepress'
 import DefaultTheme from 'vitepress/theme'
+import CopyOrDownloadAsMarkdownButtons from 'vitepress-plugin-llms/vitepress-components/CopyOrDownloadAsMarkdownButtons.vue'
 
 import './vars.css'
 import './overrides.css'
@@ -11,6 +12,7 @@ const config: Theme = {
     app.config.globalProperties.$spec = {
       version: '2.0',
     }
+    app.component('CopyOrDownloadAsMarkdownButtons', CopyOrDownloadAsMarkdownButtons)
   },
 }