Update documentation.

doc/markdown/workers/index.md

@@ -69,5 +69,16 @@ Moreover, you can specify systemd sockets if rspamd is invoked by systemd:
 bind_socket = "systemd:1"; # the first socket passed by systemd throught environment
 ~~~
 
+For unix sockets, it is also possible to specify owner and mode using this syntax:
+
+~~~nginx
+bind_socket = "/tmp/rspamd.sock mode=0666 owner=user";
+~~~
+
+Without owner and mode, rspamd uses the active user as owner (e.g. if started by root,
+then `root` is used) and `0644` as access mask. Please mention that you need to specify
+**octal** number for mode, namely prefixed by a zero. Otherwise, modes like `666` will produce
+a weird result.
+
 You can specify multiple `bind_socket` options to listen on as many addresses as
 you want.