Clarify that "disable bind_anon" does not disable anonymous access.

doc/guide/admin/security.sdf

@@ -125,7 +125,10 @@ by providing a valid name and password.
 An anonymous bind results in an {{anonymous}} authorization
 association.  Anonymous bind mechanism is enabled by default, but
 can be disabled by specifying "{{EX:disallow bind_anon}}" in
-{{slapd.conf}}(5).
+{{slapd.conf}}(5).  Note that disabling the anonymous bind mechanism
+does not prevent anonymous access to the directory.  To require
+authentication to access the directory, one should instead
+specify "{{EX:require authc}}".
 
 An unauthenticated bind also results in an {{anonymous}} authorization
 association.  Unauthenticated bind mechanism is disabled by default,