Improve docs and readme (#93)

[cjtu]

Several improvements suggested in #93

• added link to read more about CRS
• cleaned up code snippets to be mostly copy/paste runnable (provides required imports in each subsection of the readme/getting_started examples)
• added some tips for customizing plots and reference to the cartopy/matplotlib docs
• added a note about how crater tables aren't typically PDS standardized and how to deal with ambiguous input crater data
• added a benchmark to the end of the getting_started docs page

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.52%. Comparing base (685ac4b) to head (86b5e7a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #101   +/-   ##
=======================================
  Coverage   95.52%   95.52%           
=======================================
  Files           4        4           
  Lines         447      447           
  Branches       54       54           
=======================================
  Hits          427      427           
  Misses         11       11           
  Partials        9        9           

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