KNOWN_BUGS: --upload-file . hang if delay in STDIN

Closes #2051

docs/KNOWN_BUGS

@@ -38,6 +38,7 @@ problems may have been fixed or changed somewhat since this was written!
  4.1 -J with %-encoded file nameas
  4.2 -J with -C - fails
  4.3 --retry and transfer timeouts
+ 4.4 --upload-file . hang if delay in STDIN
 
  5. Build and portability issues
  5.1 Windows Borland compiler
@@ -283,6 +284,13 @@ problems may have been fixed or changed somewhat since this was written!
  https://curl.haxx.se/mail/lib-2008-01/0080.html and Mandriva bug report
  https://qa.mandriva.com/show_bug.cgi?id=22565
 
+4.4 --upload-file . hangs if delay in STDIN
+
+ "(echo start; sleep 1; echo end) | curl --upload-file . http://mywebsite -vv"
+
+ ... causes a hang when it shouldn't.
+
+ See https://github.com/curl/curl/issues/2051
 
 5. Build and portability issues