include.d: explain headers not printed prior 7.75.0

[pszlazak]

Prior to 7.75.0 response headers were not printed if -f/--fail was used and an error was reported by server.

This is NOK example for curl 7.74.0:

$ curl -q "http://httpbin.org/status/500" --include --fail
curl: (22) The requested URL returned error: 500 INTERNAL SERVER ERROR

This is OK example for curl 8.1.2:

$ curl -q "http://httpbin.org/status/500" --include --fail
HTTP/1.1 500 INTERNAL SERVER ERROR
Server: gunicorn/19.9.0
Date: Fri, 08 Sep 2023 15:15:43 GMT
Connection: keep-alive
Content-Type: text/html; charset=utf-8
Access-Control-Allow-Origin: *
Access-Control-Allow-Credentials: true
Content-Length: 0

curl: (22) The requested URL returned error: 500

This behavior was fixed in ab525c0 (precedes 7.75.0).

[bagder]

Thanks!