chore: update docs

Author: Gruak

docs/openapi-fetch/api.md

@@ -36,6 +36,7 @@ client.GET("/my-url", options);
 | `querySerializer` | QuerySerializer                                                   | (optional) Provide a [querySerializer](#queryserializer)                                                                                                                                                                          |
 | `bodySerializer`  | BodySerializer                                                    | (optional) Provide a [bodySerializer](#bodyserializer)                                                                                                                                                                            |
 | `parseAs`         | `"json"` \| `"text"` \| `"arrayBuffer"` \| `"blob"` \| `"stream"` | (optional) Parse the response using [a built-in instance method](https://developer.mozilla.org/en-US/docs/Web/API/Response#instance_methods) (default: `"json"`). `"stream"` skips parsing altogether and returns the raw stream. |
+| `baseUrl`         | `string`                                                          | Prefix the fetch URL with this option (e.g. "https://myapi.dev/v1/")                                                                                                                                                              |
 | `fetch`           | `fetch`                                                           | Fetch instance used for requests (default: fetch from `createClient`)                                                                                                                                                             |
 | `middleware`      | `Middleware[]`                                                    | [See docs](/openapi-fetch/middleware-auth)                                                                                                                                                                                        |
 | (Fetch options)   |                                                                   | Any valid fetch option (`headers`, `mode`, `cache`, `signal`, …) ([docs](https://developer.mozilla.org/en-US/docs/Web/API/fetch#options))                                                                                         |