Add usage examples for middleware to README

[ondrejsevcik]

Add practical usage examples to the README demonstrating how to use the library with various middleware patterns. The following examples should be included:

---

Use case: Console logging / error reporting tool

const logToConsole: MiddlewareFn = (next) => (request) => {
    console.log("Request", request);

    return next(request).then(async (response) => {
        console.log("Response", response);
        return response;
    });
};

---

Use case: Add authentication token to requests

const addCustomHeader = (next: RequestFetchLike) => (request: Request) => {
	const token = getToken();
	request.headers.set('authentication', `Bearer ${token}`);
  return next(request);
}

---

Use case: Throw error on 4xx or 5xx response

const errorOnNotOkResponse = (next: RequestFetchLike) => (request: Request) => {
  return next(request).then(async response => {
    if (!response.ok) {
      throw new Error(`Response status ${response.status}`);
    }
    return response;
  });
}

---

Use case: Refresh token on 401 Unauthorized response

const refreshTokenOnUnauthorizedResponse = (next: FetchLike) => (request: Request) => {
	let hasRetried = false

	return next(request).then(async (response) => {
		if (response.status === 401 && !hasRetried) {
			hasRetried = true

			await refreshToken();
			// Replay the request one more time
			return next(request)
		}
		return response
	})

---

Use case: Retry with delay on first fail

const retry = (timeout: number) => (next: Next) => (request: Request) => {
  const checkIfFail = async request => !request.ok ? throw new Error('retry') : request
  let retried = false;
  const retry = async (error) => {
    if (retried) return error;
    retried = true;
    // wait a bit
    await timeout(timeout);
    // Replay the request
    return next(request);
  } 
  return next(request).then(checkIfFail).catch(retry);
}

---

These examples will help users understand how to leverage middleware for common use cases such as logging, authentication, error handling, token refresh, and retries.