Note _bootdrv change in release-notes

doc/release-notes.txt

@@ -70,6 +70,8 @@ Emulator improvements:
   - Fix: "Show parent" items missing from TeraDesk folder windows
   - Fix: Curly braces are valid GEMDOS file name characters
   - Fix: Incorrect file match when (valid) file name contains '+'
+  - Fix: Re-apply "_bootdrv" value for GEMDOS HD on GEMDOS init
+    (as most TOS versions clear it on cold reset with "--fast-boot off")
   - When Atari file name matches multiple host files, prefer
     (potentially) truncated file name matches over ones where
     invalid chars have (potentially) been replaced with '+'