[Docs]: directory deployment docs are lacking config info

[keraron]

Issue Description

during docker compose deployment:

Error: failed to create server: oasf_api_validation.schema_url must be set when API validation is enabled (disable=false). Set it in Helm chart values.yaml or via DIRECTORY_SERVER_OASF_API_VALIDATION_SCHEMA_URL environment variable

Prposed Solution

Update docs based on https://github.com/agntcy/dir/blob/main/server/README.md

Affected Component

Directory

Checklist

• I have read the contributing guidelines.
• I have verified this does not duplicate an existing issue.