how to add header to CSV file

private void button1_Click(object sender, EventArgs e)
{
    string strValue = string.Empty;

    for (int i = 0; i < dataGridView1.Rows.Count - 1; i++)
    {
        for (int j = 0; j < dataGridView1.Rows[i].Cells.Count; j++)
        {
            if (!string.IsNullOrEmpty(dataGridView1[j, i].Value.ToString()))
            {
                if (j > 0)
                    strValue = strValue + "," + dataGridView1[j, i].Value.ToString();
                else
                {
                    if (string.IsNullOrEmpty(strValue))
                        strValue = dataGridView1[j, i].Value.ToString();
                    else
                        strValue = strValue + Environment.NewLine + dataGridView1[j, i].Value.ToString();
                }
            }
        }
                
    }
           
            
    string strFile = "c:\\Active Dir File.csv";
    File.WriteAllText(strFile, strValue);
    MessageBox.Show("File Saved in C:");
}