Update README to explain new feature

[askdkc]

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[what-the-diff]

PR Summary

• Added a new configuration option for CSV delimiter
  A new setting set_delimiter has been introduced, allowing users to specify a different delimiter for CSV files, such as ;. By default, , is the delimiter.

• Updated explanation for file upload size option
  Clarified that the file_upload_size option can be configured in the livewire config file.

• Improved instructions for publishing CSV import screen design views
  Provided better guidance on how to publish the views for customizing the CSV import screen design.

• Enhanced Japanese translation in README
  The new set_delimiter configuration option has been added to the Japanese translation of README-ja.md.