doc: extend key.id description

doc/configuration.rst

@@ -117,7 +117,7 @@ See following examples and :ref:`ACL section`.::
 ::
 
     key:
-      - id: key1
+      - id: key1                  # The real TSIG key name
         algorithm: hmac-md5
         secret: Wg==
 

doc/man/knot.conf.5in

@@ -322,6 +322,14 @@ key:
 .SS id
 .sp
 A key name identifier.
+.sp
+\fBNOTE:\fP
+.INDENT 0.0
+.INDENT 3.5
+This value MUST be exactly the same as the name of the TSIG key on the
+opposite master/slave server(s).
+.UNINDENT
+.UNINDENT
 .SS algorithm
 .sp
 A key algorithm.

doc/reference.rst

@@ -344,6 +344,10 @@ id
 
 A key name identifier.
 
+.. NOTE::
+   This value MUST be exactly the same as the name of the TSIG key on the
+   opposite master/slave server(s).
+
 .. _key_algorithm:
 
 algorithm