Cygwin: Document several fixes for signal handling in release note

Author: tyan0

winsup/cygwin/release/3.5.5

@@ -57,3 +57,7 @@ Fixes:
 
 - Fix losing signals during setjmp/longjmp.
   Addresses: https://cygwin.com/pipermail/cygwin/2024-November/256808.html
+
+- Fix several problems triggered when a lot of SIGSTOP/SIGCONT signals
+  are received rapidly.
+  Addresses: https://cygwin.com/pipermail/cygwin/2024-November/256744.html