docs: streamline and standardize docs (#687)

To ensure ongoing quality and consistency across all SDKs, the README
has been streamlined to the essentials: **Documentation**,
**Installation**, **Getting started**, **Requirements**,
**Contributing**, and **License**.

The deeper, more detailed documentation — including streaming, streaming
helpers, request & response types, counting tokens, MCP helpers, message
batches, tool use, file uploads, error handling, request IDs, retries,
timeouts, long requests, auto-pagination, default headers, advanced
usage (raw response access, logging, custom/undocumented requests, fetch
client customization, proxies), beta features, and more — now lives at
[platform.claude.com/docs/en/api/sdks/typescript](https://platform.claude.com/docs/en/api/sdks/typescript),
where it can be maintained in one place, kept up to date, and shared
across all SDK languages.

This keeps the README focused and approachable for new users while
giving experienced developers a single, authoritative source for the
full SDK documentation.

---------

Co-authored-by: stainless-app[bot] <142633134+stainless-app[bot]@users.noreply.github.com>
Co-authored-by: Felix Becker <felix@anthropic.com>
Co-authored-by: Packy Gallagher <packy@anthropic.com>

Author: 4 people

CONTRIBUTING.md

@@ -1,3 +1,7 @@
+## Contributing to documentation
+
+The documentation for this SDK lives at [platform.claude.com/docs/en/api/sdks/typescript](https://platform.claude.com/docs/en/api/sdks/typescript). To suggest changes, open an issue.
+
 ## Setting up the environment
 
 This repository uses [`yarn@v1`](https://classic.yarnpkg.com/lang/en/docs/install).