Default Review CLI interface / Add walkthrough in Custom React docs page

[pringshia]

Mostly docs as mentioned in the title.

Also updates the review CLI to ship with a default view when no local interface path is specified. This makes for a much smoother, batteries-loaded initial user experience.

# In practice this means you can now just run this (no REVIEW_APP_DIR arg):
mephisto review --db custom-react-tutorial-iterating --stdout --all

# instead of something like this
mephisto review review-app/build/ --db custom-react-tutorial-iterating --stdout --all

[codecov-commenter]

Codecov Report

Merging #697 (31d37ce) into main (a6eed61) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #697   +/-   ##
=======================================
  Coverage   63.13%   63.13%           
=======================================
  Files          86       86           
  Lines        8295     8295           
=======================================
  Hits         5237     5237           
  Misses       3058     3058           

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[JackUrb]

I love the default reviewer, and thanks for updating the docs with it!