Document all columns returned by `get_fx_groups()`

[Aariq]

I think it would be good to create a short vignette that just describes what each of the functional groups is. This would be paraphrased from Pankow & Asher. I think this is important because a couple of them have very particular definitions that you might not just guess from the column name.

[Aariq]

The vignette/article could also include drawings of SMARTS strings used. Drawings can be generated with SMARTS.plus API: https://smarts.plus/rest