Some links is 404 in README

[yansheng836]

Part of the link on the home page is 404, I guess it is caused by the project's migration to Apache, I suggest replacing it as a whole.

like the roadmap link is 404:

https://github.com/orgs/cloudberrydb/discussions/369

[tuhaihe]

Hi @yansheng836 the latest link should be #369 now.

[tuhaihe]

We're working on a new site - apache/cloudberry-site#170. Once this PR is merged, the new website will go live.

[yansheng836]

Thanks.