Fix issue with adding pa11y plugin

[alexfinnarn]

In #23, I tried to add both the lighthouse and pa11y components of the cypress-audit package. The maintainer(s) split out the packages for some reason, but it seems like the pa11y package has less to it and not great docs.

Acceptance Criteria:

• Add an example test for pA11y - example added but still broken - see cy.pa11y() fails with "Failed to fetch browser webSocket URL from http://localhost:65406/json/version" mfrachet/cypress-audit#172
• Fix issue with remote port - see this PR adding cypress-audit and examples #25
• Add example to docs section