manage: expand the 'libcurl support required' message

Example of old text:

 --dns-ipv4-addr requires that libcurl is built to support c-ares.

New version:

 For --dns-ipv4-addr to work, it requires that the underlying libcurl is
 built to support c-ares.

Closes #19665

scripts/managen

@@ -854,7 +854,7 @@ sub single {
 
     if($requires) {
         my $l = manpageify($long, $manpage);
-        push @foot, "$l requires that libcurl".
+        push @foot, "For $l to work, it requires that the underlying libcurl".
             " is built to support $requires.\n";
     }
     if($mutexed) {