Update 10min.rst
Adding article an before the word object to solve grammatical mistakes on documentation

Hi @CrazyCat-Cyber 

Thanks for your PR, but it's also correct as it is

If you're looking to contribute, that's great! Please look [here](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#where-to-start) for how/where to start, feel free to reach out if you want/need help

closing for now then