ENH: Add number of missing values and cardinality to df.describe()
It would be really handy to have the number of missing values as well as the cardinality, i.e. the lenght of df.x.value_counts() for each column x in the describe table. 

Count is indirectly reflecting this value, but ultimatily you have to think about the corner and first calculate the length of the dataframe before it leads to the numbe of missing values. 

The cardinality is important for categorical features. 