Added hcrystallball to useful packages list

Author: pybokeh

PyData/UsefulPackages.txt

@@ -43,6 +43,7 @@ PmProphet: https://github.com/luke14free/pm-prophet
 pyflux: time series library: https://github.com/RJT1990/pyflux
 sktime: https://github.com/alan-turing-institute/sktime
 darts: https://github.com/unit8co/darts
+hcrystalball: https://github.com/heidelbergcement/hcrystalball
 
 # For survival analysis, modeling churn and conversion rates
 lifelines: survival analysis: https://github.com/CamDavidsonPilon/lifelines