Add GSoC link in Wechaty Doc sidebar

[lijiarui]

Thanks for @howl-anderson organizing Wechaty GSoC 2022 add the useful material here https://github.com/wechaty/wechaty.js.org/pull/1489/files

Well, our doc sidebar seems can't find this link, it only appears on the index page, I suggest creating a PR for GSoC 2022 in the doc sidebar

[huan]

Yes, we definitely should add GSoC'22 to the sidebar!