Added discussion locations (#529)

Author: AngelOnFira

content/posts/newsletter-019/index.md

@@ -838,12 +838,10 @@ Want something mentioned in the next newsletter?
 Also, subscribe to [@rust_gamedev on Twitter][@rust_gamedev]
 or [/r/rust_gamedev subreddit][/r/rust_gamedev] if you want to receive fresh news!
 
-<!--
-TODO: Add real links and un-comment once this post is published
-**Discussions of this post**:
-[/r/rust](TODO),
-[twitter](TODO).
--->
+**Discuss this post on**:
+[/r/rust](https://www.reddit.com/r/rust_gamedev/comments/m0n8rn/this_month_in_rust_gamedev_19_february_2021/),
+[Twitter](https://twitter.com/rust_gamedev/status/1369004435280715789),
+[Discord](https://discord.gg/yNtPTb2).
 
 [/r/rust_gamedev]: https://reddit.com/r/rust_gamedev
 [@rust_gamedev]: https://twitter.com/rust_gamedev