doc: add minimum required Linux Kernel to release-notes

Author: fanquake

Diff for: doc/release-notes-empty-template.md

@@ -36,9 +36,9 @@ Compatibility
 ==============
 
 Bitcoin Core is supported and extensively tested on operating systems
-using the Linux kernel, macOS 11.0+, and Windows 7 and newer.  Bitcoin
+using the Linux Kernel 3.17+, macOS 11.0+, and Windows 7 and newer. Bitcoin
 Core should also work on most other Unix-like systems but is not as
-frequently tested on them.  It is not recommended to use Bitcoin Core on
+frequently tested on them. It is not recommended to use Bitcoin Core on
 unsupported systems.
 
 Notable changes