Request: show datetime percentiles in 'describe' method
Would be nice if `pandas.Series.describe` would show percentiles of `datetime` dtypes in the same way it does for other numeric types:
```python
import pandas as pd
dt_list = [
    "2019-01-01 00:01:00",
    "2019-01-01 00:02:00",
    "2019-01-01 00:02:10",
    "2019-01-01 00:10:01",
    "2019-01-01 00:11:00"
]
s = pd.to_datetime(pd.Series(dt_list))
s.describe()
```
```
count                       5
unique                      5
top       2019-01-01 00:02:00
freq                        1
first     2019-01-01 00:01:00
last      2019-01-01 00:11:00
dtype: object
```
```python
s.describe(percentiles = [0.25, 0.5, 0.75])
### doesn't show percentiles
```

Compare to R:
```r
dt <- c(
	"2019-01-01 00:01:00",
	"2019-01-01 00:02:00",
	"2019-01-01 00:02:10",
	"2019-01-01 00:10:01",
	"2019-01-01 00:11:00"
)
summary(as.POSIXct(dt))
```
```
                 Min.               1st Qu.                Median                  Mean               3rd Qu.                  Max. 
"2019-01-01 00:01:00" "2019-01-01 00:02:00" "2019-01-01 00:02:10" "2019-01-01 00:05:14" "2019-01-01 00:10:01" "2019-01-01 00:11:00"
```