Update ToC schema README example explanation

[cphbrt]

Super minor. This example JSON and explanation are great.

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The example mentioned "in-network-file-2.json" as the in-network file differentiating Plan C from Plan A and Plan B. The actual name of the differentiating file is "BH-health-shared-0002.json". No file named "in-network-file-2.json" is mentioned in the example JSON.

[shaselton-usds]

Whoops, thanks! Awesome catch.