docs: swap flat and legacy config doc locations

[MikeMcC399]

Issue

Currently documentation for the deprecated legacy eslintrc configuration is maintained in the README document. The documentation for flat configuration is contained in the FLAT-CONFIG document. Flat configuration should however be prioritized above the deprecated legacy eslintrc configuration.

Background

The ESLint blog eslintrc removed in ESLint v10.0.0 dated Oct 10, 2023 announced:

When ESLint v10.0.0 is released (end of 2024 or early 2025 in all likelihood), the eslintrc configuration system will be completely removed.

Additionally, if ESLint 9.1 or later is run using an eslintrc configuration, a warning similar to the following is output:

(node:25528) ESLintRCWarning: You are using an eslintrc configuration file, which is deprecated and support will be removed in v10.0.0. Please migrate to an eslint.config.js file. See https://eslint.org/docs/latest/use/configure/migration-guide for details.
(Use node --trace-warnings ... to show where the warning was created)

Change

To prepare for removal of eslintrc configurations and to raise the status of flat configurations as the preferred mode for the current version of the plugin:

• move flat config information into the README
• move eslintrc config information into a new ESLINTRC-CONFIG.md document

[cypress-app-bot]

• Create a Draft Pull Request if your PR is not ready for review. Mark the PR as Ready for Review when you're ready for a Cypress team member to review the PR.

[MikeMcC399]

@jennifer-shehane

Could you please add a new label documentation to this repo?

[jennifer-shehane]

Thanks!

[cypress-app-bot]

🎉 This PR is included in version 4.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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