improve test readme (#582)
improve test readme (#582)

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### Platforms affected


### What does this PR do?


### What testing has been done on this change?


### Checklist
- [ ] [Reported an issue](http://cordova.apache.org/contribute/issues.html) in the JIRA database
- [ ] Commit message follows the format: "CB-3232: (android) Fix bug with resolving file paths", where CB-xxxx is the JIRA ID & "android" is the platform affected.
- [ ] Added automated test coverage as appropriate for this change.

apache/cordova-android,apache/cordova-android,apache/cordova-android