Added Jupiter notebook with Digits tutorial

[zapaishchykova]

https://umap-learn.readthedocs.io/en/latest/basic_usage.html#digits-data

[coveralls]

Coverage remained the same at 94.565% when pulling b778eba on zapaishchykova:master into 834184f on lmcinnes:master.

[lmcinnes]

Hi, thanks for the PR. It would perhaps be beneficial if the notebooks were in the notebooks directory rather than at the root level. I'm also on vacation right now so I haven't had time to check the notebooks themselves too carefully.

[sleighsoft]

Tried running it but it throws an error for me at

digits_df = pd.DataFrame(digits.data[:,:10])
digits_df['digit'] = pd.Series(digits.target).map(lambda x: 'Digit {}'.format(x))

sns.pairplot(digits_df, hue='digit', palette='Spectral');

LinAlgError: singular matrix

@zapaishchykova Can you try it on a fresh install of UMAP? And maybe it is better to fix the versions in the notebook. You could add !pip install scikit=... commands into the notebook so the notebook is independent from the current master and can be manually updated when everything is confirmed to work.