Add note about native Windows bootstrap using Cygwin.

Changelog

@@ -13,6 +13,7 @@ User interface:
   (Andrew Aladjev, Urs Janssen)
 
 Platforms:
+- Bootstrap native Windows 32/64 compiler using Cygwin+gcc (Christian Jullien)
 - new AARCH64 (arm64) target (Edmund Grimley Evans)
 - vastly improved support for ARM hard float calling convention
    (Thomas Preud'homme, Daniel Glöckner)

RELICENSING

@@ -46,6 +46,7 @@
  TK                         ?                   tcccoff.c c67-gen.c
  Urs Janssen                YES
  waddlesplash               YES
+ Christian Jullien          YES                 Windows Cygwin build and tests
 
 
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