Enhance twoSum function for readability and documentation

[Vignesh-Jothi]

• Renamed the function to two_sum_indices for better readability and adherence to Python naming conventions.
• Added a detailed docstring to the function, explaining its purpose, parameters, and return value.
• Improved variable names to enhance code comprehension.
• Included comments for better explanation of each step in the solution.
• Utilized more user-friendly messages for input and output in the main function.
• Encapsulated the code in a try block to gracefully handle potential input errors.
• Added a default input in case of a ValueError during user input.

PR Checklist:

• [x] My submission is formatted according to the guidelines in the contributing guide
• [x] My addition is on refer on the language README.md file
• [x] My addition does not have a spelling problem
• [x] My submission has a proper and user-friendly description of the algorithm

What kind of change does this PR introduce? (check at least one)

• [x] Code style update
• [x] Refactor
• [x] Documentation

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