def add_ndvi(image):
    """Calculates Landsat 8 NDVI and adds NDVI band to image.

    Parameters
    ----------
    image : ee.Image
        Input image (Landsat 8).

    Returns
    -------
    N/A : ee.Image
        Input image with NDVI band added to list of bands.

    Example
    -------
        >>> import ee
        >>> peak_green = ee.Image('LANDSAT/LC08/C01/T1_SR/LC08_008057_20170602'
        >>> peak_green_ndvi = add_ndvi(peak_green)
        >>> ndvi_band = peak_green.select('NDVI')
    """
    # Calculate NDVI
    ndvi = image.normalizedDifference(['B5', 'B4']).rename('NDVI')

    # Return image with NDVI band
    return image.addBands(ndvi)