Test resources directory description

Directory test/resources keeps the following items related to tests of Jenkins pipelines and classes:

• callStacks/** - expected call stacks of Jenkins pipelines and classes. See its Readme file for more details
• org/example/** - other subdirectories follow standard structure of Java/Groovy packages.
  For example, if your test class org.example.FooSpec needs Jenkinsfile to execute and assert that results are correct, place it in org/example/FooSpec.Jenkinsfile file.