Describe correct schema generation procedure

[oskar-gmerek]

We need to improve README.md to clearly describe how to generate the schema using the better-auth CLI. It should also point out that the generated schema is intended as a starting point for further modifications. Standard better-auth instructions for schema generation are designed for native adapters and can break optimizations made specifically for SurrealDB (such as Record Links). This is to prevent misuse from being reported as a bug (see #18 ).

TODO:

• Add a section in README.md about schema generation via CLI.
• Add a warning/note that CLI-generated schema requires manual review and should be taken as a starting point for any further modifications (if needed).
• Link to issue accountId incorrectly converted to record<user> for credential authentication #18 as an example of potential pitfalls.