docs: add mocha instructions to readme

[MikeMcC399]

• closes .only and .skip rule needs #180

Issue

Users have requested linting support to detect .only and .skip constructs in Cypress test specs and have submitted issues and PRs to have these rules built in to eslint-plugin-cypress. Adding these rules into the Cypress plugin would however duplicate the following existing working and comprehensive rules in eslint-plugin-mocha:

• mocha/no-exclusive-tests to warn about the use of describe.only, it.only, suite.only, test.only, context.only and specify.only within the source code.
• mocha/no-skipped-tests to warn about the use of describe.skip, it.skip, suite.skip, test.skip, context.skip, specify.skip, xdescribe, xit, xcontext and xspecify within the source code.

The alternative to adding the rules to eslint-plugin-cypress is to install and use eslint-plugin-mocha together with eslint-plugin-cypress.

Change

A section is added to the README to describe how to use the eslint-plugin-mocha plugin together with the eslint-plugin-cypress plugin in order to detect .only and .skip usage.

Verification

Verify using the working example of eslint-plugin-cypress and eslint-plugin-mocha in the cypress-io/cypress-example-kitchensink repo (see .eslintrc for the ESLint 8.x config file).

git clone https://github.com/cypress-io/cypress-example-kitchensink
cd cypress-example-kitchensink
npm ci
npm install eslint@8 eslint-plugin-mocha@latest -D

Modify the file cypress/e2e/2-advanced-examples/actions.cy.js to add an exclusive test and a skipped test:

• Change context to context.only
• Change the first occurence of it to it.skip

and execute:

npx eslint cypress

confirm that linting errors are reported:

$ npx eslint cypress

   3:9  error    Unexpected exclusive mocha test  mocha/no-exclusive-tests
  10:6  warning  Unexpected skipped mocha test    mocha/no-skipped-tests

✖ 2 problems (1 error, 1 warning)

[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.

[jennifer-shehane]

This is great to include

[cypress-app-bot]

🎉 This PR is included in version 3.0.0 🎉

The release is available on:

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

Your semantic-release bot 📦🚀