add changelog

Author: chelseakomlo

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 BUG FIXES:
  * core: Fix search endpoint forwarding for multi-region clusters [[GH-3680](https://github.com/hashicorp/nomad/issues/3680)]
+ * core: Allow upgrading/downgrading TLS via SIGHUP on both servers and clients [[GH-3492](https://github.com/hashicorp/nomad/issues/3492)]
  * core: Fix an issue in which batch jobs with queued placements and lost
    allocations could result in improper placement counts [[GH-3717](https://github.com/hashicorp/nomad/issues/3717)]
  * config: Revert minimum CPU limit back to 20 from 100.