Move the Documentation From README.md to the Documentation Site

[koic]

Move the documentation that had grown to 3,000+ lines in README.md onto https://ruby.sdk.modelcontextprotocol.io and slim the README down to a quick start and feature overview, following the Python SDK layout:

• Add 21 server pages as the docs/_server/ collection (overview plus transports, discovery, tools, prompts, resources, roots, sampling, elicitation, multi round-trip results, notifications, notification subscriptions, cancellation, progress, ping, completions, logging, pagination, server context, configuration, and custom methods), 8 client pages as the docs/_client/ collection (overview, transports, lifecycle, multi round-trip results, cancellation, ping, pagination, and authorization), and 3 extension pages as the docs/_extensions/ collection (capability extensions and MCP Apps, following the Extensions Overview recommendation that SDK documentation list the supported extensions) - one page per topic, ordered to match the sidebar of the 2026-07-28 specification, with the client-side APIs (pinging, cancelling, and paginating from MCP::Client) documented under Building Clients
• Add top-level Examples and Protocol Versions pages after Installation, linking the runnable examples in examples/ and summarizing the supported protocol versions, the era model, and client negotiation
• Render the three sections as just-the-docs collections, which list every page beneath a plain category heading in the sidebar with no folding, and serve every page at an extensionless URL under /server/, /client/, and /extensions/, matching the sibling SDK documentation sites
• Replace docs/building-servers.md and docs/building-clients.md with redirects to the new section overview pages via jekyll-redirect-from, redirect the previously published /installation.html to its extensionless URL, fold their content that was missing from README.md into the new pages, and update the Tool argument keys reference comment in lib/mcp/server.rb to the relocated Tools page
• Reduce README.md to the badges, installation instructions, a stdio server and client quick start, a link-free feature overview in the Python SDK style, the conformance testing section, and a License section, using absolute URLs for the remaining repository links so they resolve on rubygems.org
• Adapt formatting where GitHub rendering habits break on the site: convert the numbered "three ways to define" lists into headings, since kramdown restarts numbering at 1 when code blocks split list items, convert GitHub-style alerts into just-the-docs callouts with the SEP-2260 server-to-client association note raised to a red warning, merge the duplicated Exception Reporting and Configuration Block Data sections into the Configuration page, and relocate the Streamable HTTP settings that were nested under the Logging section into the Transports page
• Refresh the migrated content against the current implementation: correct stale claims and broken examples the README carried, note on each session-era feature how it relates to the modern lifecycle of MCP 2026-07-28, and point spec links at the latest revision, keeping deliberate 2025-11-25 pins for pages the modern revision removed
• Style the site after the Rails API documentation palette (red links and accents on neutral surfaces) with matching light and dark color schemes, center the sidebar and content as one block, add a Previous/Next footer pager following the sidebar order, open external links in a new tab, and serve the MCP logo as the favicon

Every code block and heading from the previous README was verified to have a home in the new docs pages or the slimmed README before the reduction; a few examples were corrected rather than copied, as noted above.

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