Giscus (#209)

* Test giscus on homepage

* Use @giscus/react and support light theme

* Track prefers color scheme

* Create a discussion tab for each version

src/app/components/index.ts

@@ -5,6 +5,7 @@ export * from './BtnMenu'
 export * from './ErrorPanel'
 export * from './forms'
 export * from './generator'
+export * from './Giscus'
 export * from './Header'
 export * from './Icons'
 export * from './Octicon'