Doc update: how to add values to the dropdowns in VS

[sayedihashimi]

To add to the third dropdown

{
    "tags": [
        {
        "type": "projectType",
        "add": [ "ProjectType1", "ProjectType2" ],
        "remove": [ "ProjectTypeinTemplate.jsonthatyoudonotwantinVS" ]
        }
    ]
}

To add to the second dropdown

{
    "tags": [
        {
        "type": "platform",
        "add": [ "Windows", "Linux" ]
        }
    ]
}