Document one ISO source and its quirks

[AshutoshVJTI]

Context

Each ISO publishes queue data differently. Contributor docs should explain source quirks so future parser changes are safer.

Scope

Pick one market and add a short source note to the README or a new docs section.

Acceptance criteria

• Includes source link.
• Notes file/API format.
• Notes one known limitation or field normalization issue.

Helpful files

• README.md
• services/fetcher