[Ldap] minor: better query string docs

Author: Simperfit

security/ldap.rst

@@ -313,12 +313,9 @@ providers with different ``base_dn``. The value of this option must be a valid
 search string (e.g. ``uid="{username}"``). The placeholder value will be
 replaced by the actual username.
 
-When this option is used, ``dn_string`` has to be updated accordingly. Following
-the previous example, if your users have the following two DN:
-``dc=companyA,dc=example,dc=com`` and ``dc=companyB,dc=example,dc=com``, then
-``dn_string`` should be ``dc=example,dc=com``. If the ``query_string`` option is
-``uid="{username}"``, then the authentication provider can authenticate users
-from both DN.
+When this option is used, ``query_string`` will search in the DN specified by ``dn_string``
+and the DN resulted of the ``query_string`` will be used to authenticate the user with
+his password.
 
 Bear in mind that usernames must be unique across both DN, as the authentication
 provider won't be able to select the correct user for the bind process if more