Add crystal structure column

[madsfaerch]

Hi again,

I think it would be nice to include a crystal structure column in the dataset.
Crystal structures are available for all elements, except for 113-117, which is great.

I propose using data from Wikipedia's article Periodic table (crystal_structure)

[andrejewski]

I appreciate your enthusiasm. I have no problem adding more accurate information to the dataset. If you have a few minutes tomorrow to talk, I'd have no problem making you a contributor to the project. Let me know, my email is [email protected]. Or if you'd like to PR and move on with your life too that's fine.

[sabidhasan]

@andrejewski

Hello, just came across this repo and as a chemist-dabbling-in-coding, I'd love to help with some issues.

Please let me know if I can do this crystal structure column - if so, I can fork and make a PR, or if you want to discuss, I am open to that as well.