feat(docs/{index,meetup-2-guide}): extract group info

- Moved Telegram/Matrix group information to meetup guide
- Redirected group information button on index page

Signed-off-by: Noa Virellia <noa@requiem.garden>

src/content/docs/index.mdx

@@ -10,12 +10,7 @@ hero:
         - text: 'Meetup #2 参会指南'
           link: /meetup-2-guide
           icon: right-arrow
-        - text: 加入 Telegram 活动群组
-          link: https://t.me/nixcnmeetup
-          icon: external
-          variant: minimal
-        - text: 加入 Matrix 活动群组
-          link: https://matrix.to/#/#nix-cn-meetup:rebmit.moe
-          icon: external
+        - text: 加入活动群组
+          link: /meetup-2-guide#%E6%B4%BB%E5%8A%A8%E7%BE%A4%E7%BB%84
           variant: minimal
 ---