message: Add RFC 19 to the summary
  Add RFC 19 to the summary
diff: - [RFC-0016: Supporting Flexible Checksums](./rfcs/rfc0016_flexible_checksum_support.md)
  - [RFC-0017: Customizable Client Operations](./rfcs/rfc0017_customizable_client_operations.md)
  - [RFC-0018: Logging in the Presence of Sensitive Data](./rfcs/rfc0018_logging_sensitive.md)
  + - [RFC-0019: Event Streams Errors](./rfcs/rfc0019_event_streams_errors.md)
  - [Contributing](./contributing/overview.md)
  - [Writing and debugging a low-level feature that relies on HTTP](./contributing/writing_and_debugging_a_low-level_feature_that_relies_on_HTTP.md)
  