update whatsnew

Author: wholmgren

docs/sphinx/source/whatsnew/v0.3.3.txt

@@ -35,6 +35,11 @@ Bug fixes
 * Fix snlinverter and singlediode documentation. They incorrectly said that
   inverter/module must be a DataFrame, when in reality they can be any
   dict-like object. (:issue:`157`)
+* Propagate airmass data through ModelChain's get_irradiance call so that
+  the perez model can use it, if necessary. (:issue:`172`)
+* Fix problem in which the perez function dropped nighttime values.
+  Nighttime values are now set to 0.
+  (:issue:`191`)
 
 
 Documentation