include.d: explain headers not printed with --fail before 7.75.0

Prior to 7.75.0 response headers were not printed if -f/--fail was used
and an error was reported by server.  This was fixed in ab525c0
(precedes 7.75.0).

Closes curl#11822

docs/cmdline-opts/include.d

@@ -14,3 +14,6 @@ include things like server name, cookies, date of the document, HTTP version
 and more...
 
 To view the request headers, consider the --verbose option.
+
+Prior to 7.75.0 curl did not print the headers if --fail was used in
+combination with this option and there was error reported by server.