Placeholder Value - Update README.md

[IlicMiljan]

Description of Changes

Updated README.md to include information on the new placeholder functionality for the #[Encrypted] attribute. This provides a clear example of specifying a placeholder for decryption failures.

How Has This Been Tested?

Documentation updates do not undergo the same testing processes.

Checklist

Please confirm the following:

• I have tested my changes and corrected any errors.
• I have documented my changes if necessary.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.67%. Comparing base (bd1e665) to head (ff48b1b).

Additional details and impacted files

@@            Coverage Diff            @@
##               main      #15   +/-   ##
=========================================
  Coverage     92.67%   92.67%           
  Complexity       72       72           
=========================================
  Files            19       19           
  Lines           232      232           
=========================================
  Hits            215      215           
  Misses           17       17           

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