Update configuring-playbook-ldap-auth.md: the link to README

Signed-off-by: Suguru Hirahara <did🔑z6MkvVZk1A3KBApWJXv2Ju4H14ErDfRGxh8zxdXSZ4vACDg5>

docs/configuring-playbook-ldap-auth.md

@@ -11,7 +11,7 @@ SPDX-License-Identifier: AGPL-3.0-or-later
 
 The playbook can install and configure the [matrix-synapse-ldap3](https://github.com/matrix-org/matrix-synapse-ldap3) LDAP Auth password provider for you.
 
-See the project's [documentation](https://github.com/matrix-org/matrix-synapse-ldap3/blob/main/README.rst) to learn what it does and why it might be useful to you.
+See the project's [documentation](https://github.com/matrix-org/matrix-synapse-ldap3/blob/main/README.md) to learn what it does and why it might be useful to you.
 
 ## Adjusting the playbook configuration