Add UPGRADING note

kocsismate · kocsismate · commit 0af607d4c8b6 · 2020-05-07T10:00:46.000+02:00
diff --git a/UPGRADING b/UPGRADING
@@ -189,6 +189,8 @@ PHP 8.0 UPGRADE NOTES
     array, resource or non-overloaded object. The only exception to this is the
     array + array merge operation, which remains supported.
     RFC: https://wiki.php.net/rfc/arithmetic_operator_type_checks
+  . Float to string casting will now always behave locale-independently.
+    RFC: https://wiki.php.net/rfc/locale_independent_float_to_string
 
 - COM:
   . Removed the ability to import case-insensitive constants from type
