roles/ipaclient/README.md: Add information about ipaclient_otp

The docuemntation of ipaclient_otp was not part of the pull request
102 (commit d1af0ff4). The role README has been updated.

roles/ipaclient/README.md

@@ -196,6 +196,7 @@ Variable | Description | Required
 -------- | ----------- | --------
 `ipaclient_use_otp` | The bool value defines if a one-time password will be generated to join a new or existing host. `ipaclient_use_otp` defaults to `no`. The enforcement on an existing host is not done if there is a working krb5.keytab on the host. If the generation of an otp is enforced for an existing host entry, then the host gets disabled and the containing keytab gets removed. | no
 `ipaclient_allow_repair` | The bool value defines if an already joined or partly set-up client can be repaired. `ipaclient_allow_repair` defaults to `no`. Contrary to `ipaclient_force_join=yes` the host entry will not be changed on the server. | no
+`ipaclient_otp` | The string value sets an already generated one-time password for the host. The role will use it and not try to generate a new one. Do not enable `ipaclient_use_otp` additionally. | no
 `ipaclient_install_packages` | The bool value defines if the needed packages are installed on the node. `ipaclient_install_packages` defaults to `yes`. | no
 `ipaclient_on_master` | The bool value is only used in the server and replica installation process to install the client part. It should not be set otherwise. `ipaclient_on_master` defaults to `no`. | no