For example, the Hard Drop community is dedicated to all variants of tetris, and make up a large percentage of the jstris playerbase. Why not send some of the people submitting here to a place where they can hone their skills?

Under, say, guides or resources would be a good place to put this.

discord.gg/harddrop

Added as discord link, thank you

Why would you not link to the official JSTris discord instead lol

If you have the link for it, I would happily add it too