Fix Issue 21222 - Add windows 64 bit version of rdmd

Author: RazvanN7

windows/d2-installer.nsi

@@ -295,6 +295,7 @@ SectionGroup /e "D2"
 
   Section "Add to PATH" AddD2ToPath
     ${EnvVarUpdate} $0 "PATH" "A" "HKLM" "$INSTDIR\dmd2\windows\bin"
+    ${EnvVarUpdate} $0 "PATH" "A" "HKLM" "$INSTDIR\dmd2\windows\bin64"
   SectionEnd