DOC: update the to_json() docstring
Fixes validation errors and adds an example for each orientation.

- [ x] PR title is "DOC: update the <your-function-or-method> docstring"
- [ x] The validation script passes: `scripts/validate_docstrings.py <your-function-or-method>`
- [ x] The PEP8 style check passes: `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x ] The html version looks good: `python doc/make.py --single <your-function-or-method>`
- [x ] It has been proofread on language by another sprint participant

```
Errors found:
	Missing description for See Also "pandas.read_json" reference
	Examples do not pass tests
```

I'm not able to make this pass.