Add documentation for CATcher's parser

[luminousleek]

Summary:

Fixes #1204

Changes Made:

• Add comment formats and examples
• Add examples for parsers that are more difficult to understand

Proposed Commit Message:

When CATcher's parsers were updated to use arcsecond, there was minimal
documentation within the codebase to explain how the parsers work. As
such, it was difficult to understand and maintain these parsers.

Let's add examples for each comment template and explain the parsers
that are more difficult to understand.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (fe7be44) 53.89% compared to head (c694926) 53.85%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1240      +/-   ##
==========================================
- Coverage   53.89%   53.85%   -0.04%     
==========================================
  Files         102      102              
  Lines        2889     2889              
  Branches      535      535              
==========================================
- Hits         1557     1556       -1     
  Misses        989      989              
- Partials      343      344       +1     

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[cheehongw]

LGTM!