feat: add slack channel

Author: zyxxoo

README.md

@@ -204,6 +204,7 @@ hugegraph-ai is licensed under [Apache 2.0 License](./LICENSE).
 
 - **GitHub Issues**: [Report bugs or request features](https://github.com/apache/incubator-hugegraph-ai/issues) (fastest response)
 - **Email**: [dev@hugegraph.apache.org](mailto:dev@hugegraph.apache.org) ([subscription required](https://hugegraph.apache.org/docs/contribution-guidelines/subscribe/))
+- **Slack**: [Join the ASF HugeGraph channel](https://the-asf.slack.com/archives/C059UU2FJ23)
 - **WeChat**: Follow "Apache HugeGraph" official account
 
 <img src="https://raw.githubusercontent.com/apache/hugegraph-doc/master/assets/images/wechat.png" alt="Apache HugeGraph WeChat QR Code" width="200"/>