Inconsistent ID format in README example vs code validation

[dhyaniarun1993]

Description

The README example under Superchain configuration shows a superchain named with a dash:

superchains:
  superchain-a:
    enabled: true
    participants: ["2151908"]

However, using superchain-a as an ID results in the following error:

Evaluation error: fail: ID cannot contain '-': superchain-a
    at [src/util/id.star:4:13]: assert_id

The code explicitly rejects - in IDs via assert_id.