import processing
rasterLyr = QgsRasterLayer("<INSERT PATH TO TIF>", "Relief")
if rasterLyr.isValid():
    param = {'INPUT':rasterLyr,
            'Z_FACTOR': 1.0,
            'AUTO_COLORS': True,
            'OUTPUT': 'INSERT OUTPUT PATH'}
    processing.run("qgis:relief", param)
    QgsProject.instance().addMapLayers([rasterLyr])