Add content to README.md - add-user

If user is not defined (add-user.sh) GWT is thrown with empty model:

Unexpected HTTP response: 403

Request
{
    "operation" => "composite",
    "address" => [],
    "steps" => [
        {
            "operation" => "read-attribute",
            "name" => "process-type",
            "address" => []
        },
        {
            "operation" => "read-attribute",
            "name" => "product-version",
            "address" => []
        },
        {
            "operation" => "read-attribute",
            "name" => "release-version",
            "address" => []
        }
    ]
}

Response

Forbidden
No details