Gargi Shaw docs CR background and PAH interactions

This updates two parts of Hazy 1 and adds a citation to Shaw & Ferland (2021arXiv210103732S). The discussion reviews how the PAH abundance affects the cosmic ray secondary ionization rate and gives the recommended Galactic background for the case where PAHs are present. Our recommended default CR background rate remains the Indriolo+ value but we give the Cloudy command to change this rate to our recommended value when PAHs are present.