update README. set password before starting opencloud

[ScharfViktor]

1. I tried to start opencloud COMPOSE_FILE=docker-compose.yml:traefik/opencloud.yml following READMI and encountered an issue in step 3 https://github.com/opencloud-eu/opencloud-compose/blob/main/README.md#local-development

2025-09-04 11:15:15 2025/09/04 09:15:15 Could not create config: config file already exists, use --force-overwrite to overwrite or --diff to show diff
2025-09-04 11:15:16 The password of service user admin has not been set properly in your config for idm. Make sure your /etc/opencloud config contains the proper values (e.g. by using 'opencloud init --diff' and applying the patch or setting a value manually in the config/corresponding environment variable).

It happens when INITIAL_ADMIN_PASSWORD is empty. Following READMI we set password later after starting docker compose up -d

Solution:

set password before starting opencloud

2. Changed bitnami/openldap:2.6 to bitnamilegacy/openldap:2.6 according Use bitnamilegacy opencloud#1418

[micbar]

We decided not to set a default admin password for security reasons.

[ScharfViktor]

We decided not to set a default admin password for security reasons.

then I will change the sequence of steps in readmi