text: Title: JOSS Review Suggested Edits
  Body: Review in openjournals/joss-reviews#1315 by @ixjlyons suggested a few minor fixes along with #164 and #165. 
  
  # JOSS Paper: 
  - [x] Typo in the paper, second paragraph: "We also an provide extensive..." -> "We also provide an extensive..."
  - [x] I think there may be some missing DOIs in the references.
  
  # KM implementation:
  - [x] I'd consider hiding `SimplicialNerve` until it's implemented.
  - [x] The last example in the `KeplerMapper.project()` docstring should probably be moved/copied to the `fit_transform()` docstring.