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/meetup-2-guide.mdx

@@ -24,6 +24,15 @@ Nix CN Meetup #2 是国内第二次以 Nix 为主题的聚会。我们希望汇
     会议名牌定制说明
 </LinkButton>
 
+## 活动群组
+
+<LinkButton href='https://t.me/nixcnmeetup' icon='telegram' variant='secondary' iconPlacement='start'>
+    Telegram 活动群组
+</LinkButton>
+<LinkButton href='https://matrix.to/#/#nix-cn-meetup:rebmit.moe' icon='matrix' variant='secondary' iconPlacement='start'>
+    Matrix 活动群组
+</LinkButton>
+
 ## 交通信息
 
 ### 抵达上海