TODO: Windows: set attribute 'archive' for completed downloads

Closes #3354

docs/TODO

@@ -149,6 +149,7 @@
  18.8 offer color-coded HTTP header output
  18.9 Choose the name of file in braces for complex URLs
  18.10 improve how curl works in a windows console window
+ 18.11 Windows: set attribute 'archive' for completed downloads
  18.12 keep running, read instructions from pipe/socket
  18.13 support metalink in http headers
  18.14 --fail without --location should treat 3xx as a failure
@@ -1004,6 +1005,17 @@ that doesn't exist on the server, just like --ftp-create-dirs.
  window, the transfer is interrupted and can get disconnected. This can
  probably be improved. See https://github.com/curl/curl/issues/322
 
+18.11 Windows: set attribute 'archive' for completed downloads
+
+ The archive bit (FILE_ATTRIBUTE_ARCHIVE, 0x20) separates files that shall be
+ backed up from those that are either not ready or have not changed.
+
+ Downloads in progress are neither ready to be backed up, nor should they be
+ opened by a different process. Only after a download has been completed it's
+ sensible to include it in any integer snapshot or backup of the system.
+
+ See https://github.com/curl/curl/issues/3354
+
 18.12 keep running, read instructions from pipe/socket
 
  Provide an option that makes curl not exit after the last URL (or even work