[infra-tests] Fix up hyperlink to testharness.js documentation in resources/readme.md following move (#5674)

@jgraham We should update the hyperlink to the testharness.js documentation in resources/readme.md following the merger of the <https://github.com/w3c/testharness.js> repository into the <https://github.com/w3c/web-platform-tests> repository.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/5674

Received on Monday, 24 April 2017 18:04:33 UTC