fix typo README.md

[VitalikBerashvili]

Title

fix typo README.md

Description

This pull request fixes a typo in the accumulator/README.md file:

• Corrected "verifiying" to "verifying" for improved clarity and accuracy.

Details of Changes

• Replaced the incorrect spelling "verifiying" with the correct version "verifying" in the description of the light tree's purpose.

Checklist

• [x] The typo has been corrected.
• [x] Changes were reviewed for accuracy.
• [x] Documentation remains consistent with the repository's standards.

Additional Notes

This change is purely editorial and does not impact any functional aspects of the repository.