Add tutorials of running and analyzing REXEE simulations

[wehs7661]

In this PR, we aim to add simple tutorials about running and analyzing standard REXEE simulations. A tutorial on MT-REXEE will be added in the future.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.38%. Comparing base (552573d) to head (18c3d03).

❗ Current head 18c3d03 differs from pull request most recent head 5daa0a5

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Additional details and impacted files

@@           Coverage Diff           @@
##           master      #52   +/-   ##
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  Coverage   98.38%   98.38%           
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  Files          10       10           
  Lines        1921     1921           
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  Hits         1890     1890           
  Misses         31       31           

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