fix(docs): use correct Parameters<T> syntax in tool examples

[lutz-grex]

The README examples used #[tool(param)] on function parameters, which is not a supported syntax and fails to compile. Replace with the Parameters<T> wrapper pattern that the macros actually expect.

Closes #812

Motivation and Context

Users copying the README tool examples get a compile error:

error: expected non-macro attribute, found attribute macro `tool`

The #[tool(param)] attribute on function parameters was never implemented. The correct pattern is Parameters<T>
with a struct deriving JsonSchema, as used in examples/servers/src/common/calculator.rs.

How Has This Been Tested?

• Copied the old README example into a standalone project - confirmed the compile error from README example cannot run #812
• Copied the fixed example - compiles clean with cargo check
• Verified the pattern matches the existing calculator example in examples/servers/src/common/calculator.rs

Breaking Changes

None

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

Both the English (README.md) and Chinese (docs/readme/README.zh-cn.md) READMEs contained the same incorrect
examples - both are fixed in this PR.