Explain relationship between pScheduler exports and pSConfig template

[mfeit-internet2]

In pSConfig's Tests section, there could stand to be a paragraph about the relationship between the output of pscheduler task --export and the JSON

E.g., the test section of this...

$ pscheduler task --export throughput --source foo --dest bar
{
    "test": {
        "spec": {
            "dest": "bar",
            "schema": 1,
            "source": "foo"
        },
        "type": "throughput"
    }
}

...gets put into a test in the pSConfig template with some parameter adjustment:

"tests": {
    "my_throughput": {
        "spec": {
            "dest": "{% address[1] %}",
            "schema": 1,
            "source": "{% address[0] %}"
        },
        "type": "throughput"
    }
}