Fix typo on README

[raphaelpra]

Fix a little typo on documentation.

Motivation and Context

It could lead to the thought that multiple notifications are sent

How Has This Been Tested?

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Breaking Changes

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Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[raphaelpra]

Duplicates of #303