Added example to Dataframe.get docs
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry
@MarcoGorelli 

you mean this one right? @MarcoGorelli
```
df2 = df1.get("key") #key column is not available in dataframe 
print(df2)
None #Returns default value if not found.
``` I think, something like this  (`df` is directly from the example you added)
```python
In [9]: df.get(["temp_celsius","windspeed","temp_Kelvin"], default = "Some column missing")
Out[9]: 'Some column missing'
``` have you run the validate_docstrings script? https://pandas.pydata.org/pandas-docs/stable/development/contributing_documentation.html#updating-a-pandas-docstring yes. Tested the `validate_docstrings` and `python make.py clean`, `python make.py --single pandas.DataFrame.get    `                    
 These errors from `validate_docstrings` need fixing:
```
	flake8 error: E231 missing whitespace after ','
2     E251 unexpected spaces around keyword / parameter equals (2 times)
```
check https://www.python.org/dev/peps/pep-0008/ @MarcoGorelli How did you remove those errors? I have tried using autopep8 in vscode, It did nothing for me. Can u please explain a bit?