docs(readme): describe rate-limit retries

Author: willleeney

README.md

@@ -415,6 +415,10 @@ Everything the SDK throws is a `StackOneError`:
 
 `timeout` (milliseconds, default 60000) bounds every MCP listing and `tools/call`, and account discovery.
 
+### Rate limits
+
+Every request the SDK makes (`GET /accounts` and every MCP request, `tools/call` included) is retried when the API answers `429 Too Many Requests`: up to 3 more times, waiting for the response's `Retry-After` (capped at 30s), or 1s, 2s, then 4s with jitter when there is none. Each retry logs a warning. A request still rate limited after that throws `StackOneAPIError` with `statusCode` `429`, and fails the whole `fetchTools()` or `search()` call: unlike a dead account, a rate-limited one is never skipped, so you never get a partial catalog. The retries' waits count towards `timeout`.
+
 ### Custom Base URL
 
 ```typescript