docs: add 3 major browser versions supportability

[MikeMcC399]

Situation

The Cypress 14.0.0 changelog includes the text:

Cypress now only officially supports the latest 3 major versions of Chrome, Firefox, and Edge - older browser versions may still work, but we recommend keeping your browsers up to date to ensure compatibility with Cypress.

This is not reflected in the Cypress Docker image documentation.

Change

Add a corresponding statement to the README > Browsers section.

Link to https://docs.cypress.io/app/references/launching-browsers#Browser-versions-supported

Cypress officially supports the latest 3 major versions of Chrome, Firefox, and Edge. We recommend using up to date Cypress Docker images for supportability.

[cypress-app-bot]

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