linkify a link

Author: SethTisue

blog/_posts/2021-12-21-discord.md

@@ -13,7 +13,7 @@ have adopted **Discord** as our official chat platform.
 **Please join us** for live text-based chat on the Scala Discord
 server, via this link:
 
-* https://discord.com/invite/scala
+* [https://discord.com/invite/scala](https://discord.com/invite/scala)
 
 The server has existed for several years now and is already
 busy and well-established.  It is actively moderated under the