[docs] Minor improvements to Compatibility Notes

Progressed from Windows Vista to Windows 7 for OS testing statement.

Author: randolf

doc/release-notes.md

@@ -48,7 +48,7 @@ Compatibility
 ==============
 
 Bitcoin Core is extensively tested on multiple operating systems using
-the Linux kernel, macOS 10.8+, and Windows Vista and later. Windows XP is not supported.
+the Linux kernel, macOS 10.8+, and Windows 7 and newer (Windows XP is not supported).
 
 Bitcoin Core should also work on most other Unix-like systems but is not
 frequently tested on them.