fix: document a low-friction way to run tests to satisfy PR template checklist item

[olets]

Expected Behavior

There's a low-friction path to satisfying the pull request template's "All new and existing tests passed." checklist item.

Current Behavior

• Testing is not documented in either ./README.md or docs/README.md.
• Dev has to know to know that the presence of yarn.lock means dependencies should be installed with yarn
• yarn test in the root directory errors

  yarn test 
  yarn run v1.22.19
  $ cross-env HOME=$PWD jest
  ● Validation Error:
  
    Test environment @commitlint/test-environment cannot be found. Make sure the testEnvironment configuration option points to an existing node module.
  
    Configuration Documentation:
    https://jestjs.io/docs/configuration
  
  error Command failed with exit code 1.
  info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
  

Affected packages

• cli
• core
• prompt
• config-angular

Possible Solution

I haven't experimented. The ignoreDeps looks relevant. Or maybe tests have to be run manually in each package in ./@commitlint?

Steps to Reproduce

# if not starting from a fresh clone, first `rm -rf node_modules`
yarn
yarn test

Context

Opening a docs change pull request, got to the "All new and existing tests passed." checklist item, and for completeness tried to run the tests.

commitlint --version

17.7.0

git --version

2.41.0

node --version

v18.16.0

[escapedcat]

Testing is somewhat documented in this part pf the docs. Happy for improvements of the docs though.