doc: document remote/no-edns option

doc/man/knot.conf.5in

@@ -1003,6 +1003,7 @@ remote:
     via: ADDR[@INT] ...
     key: key_id
     block\-notify\-after\-transfer: BOOL
+    no\-edns: BOOL
 .ft P
 .fi
 .UNINDENT
@@ -1047,6 +1048,13 @@ When incoming AXFR/IXFR from this remote (as a primary server), suppress
 sending NOTIFY messages to all configured secondary servers.
 .sp
 \fIDefault:\fP off
+.SS no\-edns
+.sp
+If enabled, no OPT record (EDNS) is inserted to outgoing requests to this
+remote server. This mode is necessary for communication with some broken
+implementations (e.g. Windows Server 2016).
+.sp
+\fIDefault:\fP off
 .SH ACL SECTION
 .sp
 Access control list rule definitions. The ACLs are used to match incoming

doc/reference.rst

@@ -1063,6 +1063,7 @@ transfer, target for a notification, etc.).
      via: ADDR[@INT] ...
      key: key_id
      block-notify-after-transfer: BOOL
+     no-edns: BOOL
 
 .. _remote_id:
 
@@ -1120,6 +1121,17 @@ sending NOTIFY messages to all configured secondary servers.
 
 *Default:* off
 
+.. _remote_no-edns:
+
+no-edns
+-------
+
+If enabled, no OPT record (EDNS) is inserted to outgoing requests to this
+remote server. This mode is necessary for communication with some broken
+implementations (e.g. Windows Server 2016).
+
+*Default:* off
+
 .. _ACL section:
 
 ACL section