DOC: ssl-load-extra-files only applies to certificates on bind lines

Be explicit about ssl-load-extra-files not applying to certificates
referenced with the crt keyword on server lines.

It must be backported in 2.2.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index a824279..c1f6f82 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -1373,7 +1373,8 @@
 
 ssl-load-extra-files <none|all|bundle|sctl|ocsp|issuer|key>*
   This setting alters the way HAProxy will look for unspecified files during
-  the loading of the SSL certificates.
+  the loading of the SSL certificates associated to "bind" lines. It does not
+  apply to certificates used for client authentication on "server" lines.
 
   By default, HAProxy discovers automatically a lot of files not specified in
   the configuration, and you may want to disable this behavior if you want to