docs: add spreadsheet-mcp to Built with rmcp

[PSU3D0]

Added 'spreadsheet-mcp' to the "Built with rmcp" section in README.md.

Motivation and Context

spreadsheet-mcp is a MCP server for spreadsheet analysis built with rmcp. It provides LLM agents with token-efficient access to XLSX workbooks through:

• Automatic region detection — Identifies data tables, parameter blocks, and output areas using gutter detection and recursive splitting
• Column profiling — Infers types, cardinality, and value distributions from small samples
• Sampling modes — Distributed/first/last sampling to read representative rows without loading entire sheets
• Region-scoped reads — Tools accept region_id to scope queries without manual range specification
• Recalculation Support — Supports recalculation via a docker-bundled Libreoffice with custom macros
• Region Screenshotting — Allows visual LLM's to visually "see" spreadsheet sections via an optional screenshot tool mimicking tools like Playwright
• Ephemeral Forks — Supports ephemeral "spreadsheet forks" that allow an LLM to edit a spreadsheet, rerun calculations, and repeat, allowing experimentation and day to day assistance

Link: spreadsheet-mcp

How Has This Been Tested?

N/A (Documentation update only)

Breaking Changes

No breaking changes.

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

spreadsheet-mcp uses rmcp for both stdio and HTTP streaming transports, exposing tools for workbook discovery, region detection, table profiling, value search, formula tracing, and more. Published on crates.io.

[PSU3D0]

Note: Updated from spreadsheet-read-mcp to spreadsheet-mcp to cover new write tooling.