[DOC] Missing root node in configuration file example

[bigfoot90]

I'm following your instructions on creating configuration file, but it seems there is missing the root node.

I've solved adding the root node in my metrics.yml
There is my working configuration

phpmetrics:
    # paths to explore
    path:
        directory: src
        extensions: php
        exclude: Features|Tests|tests

    # report and violations files
    logging:
        report:
            xml:    app/logs/metrics/phpmetrics.xml
            html:   app/logs/metrics/phpmetrics.html
            csv:    app/logs/metrics/phpmetrics.csv
        violations:
            xml:    app/logs/metrics/violations.xml
        chart:
            bubbles: app/logs/metrics/bubbles.svg

    # condition of failure
    failure: average.maintenabilityIndex < 50 or sum.loc > 10000

    # rules used for color
    rules:
        cyclomaticComplexity: [ 10, 6, 2 ]
        maintenabilityIndex: [ 0, 69, 85 ]