Enhance documentation in FractionalKnapsack

[Hardvan]

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized it.
• All filenames are in PascalCase.
• All functions and variable names follow Java naming conventions.
• All new algorithms have a URL in their comments that points to Wikipedia or other similar explanations.
• All new code is formatted with clang-format -i --style=file path/to/your/file.java

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.75%. Comparing base (dfff8d9) to head (e4dd78d).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5795      +/-   ##
============================================
+ Coverage     66.74%   66.75%   +0.01%     
  Complexity     4489     4489              
============================================
  Files           610      610              
  Lines         16929    16929              
  Branches       3267     3267              
============================================
+ Hits          11299    11301       +2     
+ Misses         5182     5181       -1     
+ Partials        448      447       -1     

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