v2.0.18-rc1

docs: update README with configurable thread pool options

Update Performance Tuning section:
- Add command line options for --aio-threads and --hashing-threads
- Update storage type recommendations with CLI examples
- Replace code editing instructions with runtime configuration
- Add testing examples for different configurations

Update Help section:
- Document all available command line options
- Include new thread pool configuration flags

Benefits:
- Users can tune performance without recompilation
- Easy testing of different configurations
- Better documentation for Phase 2 optimization

Signed-off-by: Date Huang <tjjh89017@hotmail.com>