COPYING: add the "and many contributors" text from the curl license

Makes them identically phrased.

Fixes #365
Reported-by: Carlos Henrique Lima Melara

COPYING

@@ -1,6 +1,7 @@
 COPYRIGHT AND PERMISSION NOTICE
 
-Copyright (c) 2023 - 2024, Daniel Stenberg, <[email protected]>
+Copyright (c) 2023 - 2024, Daniel Stenberg, <[email protected]>, and many
+contributors, see the THANKS file.
 
 All rights reserved.