Update README to include community invite links

Author: Conor Okus

README.md

@@ -30,8 +30,8 @@ sufficient for a developer or project to experiment with it. Recent increased
 contribution rate to the project is expected to lead to a high quality, stable,
 production-worthy implementation in 2021.
 
-Communications for Rust-Lightning and Lightning Development Kit happens through
-[LDK slack](http://lightningdevkit.org/).
+Communications for Rust-Lightning and Lightning Development Kit happens through our LDK
+[slack](https://join.slack.com/t/lightningdevkit/shared_invite/zt-tte36cb7-r5f41MDn3ObFtDu~N9dCrQ) & [discord](https://discord.gg/5AcknnMfBw) channels.
 
 About
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