Note when post_listen_callback was added

doc/src/guide/migrating_from_2.0.asciidoc

@@ -23,7 +23,7 @@ for Erlang/OTP 21 has been removed.
   programmatically shut down idle connections to
   make up space for new connections, for example.
 
-* A `post_listen` callback option has been added. It
+* A `post_listen_callback` option has been added. It
   receives sockets immediately after the `Transport:listen/1`
   call. It can be used for some additional initialization
   of the socket, such as setting file permissions on

doc/src/manual/ranch.asciidoc

@@ -194,6 +194,7 @@ documentation of the transport module you are using for more details.
 
 == Changelog
 
+* *2.1*: The `post_listen_callback` transport option was added.
 * *2.0*: The type `transport_opts(SocketOpts)` was added.
 * *2.0*: The function `ranch:accept_ack/1` was removed in favor of
          link:man:ranch:handshake(3)[ranch:handshake(3)].