docs(examples): fixing the prompts example

[Niraj-Fonseka]

Motivation and Context

The example provided under the Prompts section in the Readme doesn't work due to types not being importable from mcp.server.fastmcp. If someone is using this library for the first time, seeing this error results in bad user/developer experience

In this change, the existing example was corrected with the proper imports and tested by running locally.

How Has This Been Tested?

After the example was fixed, the example was run locally with the latest version of the library.

Breaking Changes

No

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

[dsp-ant]

Thank you