Fix Typo in README.md

[MonkeyKing44]

Pull Request Title: Fix Typo in README.md - "assignes" to "assigns"

Summary:

This pull request addresses a typo in the README.md file within the cpp/src/barretenberg/smt_verification directory to improve clarity and professionalism in the documentation:

• Corrected the spelling of "assignes" to "assigns" in the description of the set_variable_name method.

Changes Made:

• README.md:
  • Fixed the typo in the explanation of the set_variable_name method under the Standard and Ultra CircuitBuilders section.

Files Changed:

• cpp/src/barretenberg/smt_verification/README.md

Testing:

• This is a documentation-only update and does not impact the functionality or codebase.

Additional Notes:

• Accurate documentation enhances the ease of understanding for contributors and users of the project.
• This correction ensures consistency in grammar and helps maintain a professional standard.

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