docs: Add Documentation for Using #fmt: skip with Equations in Black Formatter

[uwcdc]

Summary of Changes

This PR updates the contributing.rst file to include information about the use of #fmt: skip tags for Black formatting exceptions for equations in the "caustics" project documentation.

Changes Made

Added a new section titled "Black Formatting Exceptions for Equations."
Provided information on how to use #fmt: skip for exempting specific code blocks from Black formatting.
Included best practices for using #fmt: skip with equations.
Example Usage

psi = (q2 * (x2 + self.s2) + y2).sqrt() # fmt: skip
Context

Maintaining consistent and readable code is crucial in the "caustics" project, and we use the Black code formatter for this purpose. However, there are scenarios where automatic formatting may interfere with the desired layout of equations. This PR introduces the use of #fmt: skip tags to selectively exempt equations from Black formatting.

Testing

Verified the changes locally by rendering the contributing.rst file and confirming that the new section is displayed correctly.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (5087adf) 89.51% compared to head (84e25b9) 89.51%.

Additional details and impacted files

@@            Coverage Diff             @@
##           black_doc      #64   +/-   ##
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  Coverage      89.51%   89.51%           
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  Files             36       36           
  Lines           1955     1955           
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  Hits            1750     1750           
  Misses           205      205           

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