Request for API Usage Limits and Error Documentation

# Request for API Usage Limits and Error Documentation

First of all, I want to express my appreciation for the Blockstream.info API. It's a fantastic resource for the Bitcoin community, and the fact that it's provided for free is truly commendable.

However, I've noticed that the current documentation lacks information on API usage limits and potential error responses. This information would be incredibly valuable for developers to ensure we're using the API responsibly and handling errors correctly.

Specifically, I would appreciate clarity on:

1. Are there any rate limits or usage quotas for the API?
2. What are the possible error responses for different endpoints?
3. For the `/address/:address` endpoint, what specific errors might be returned for an invalid or non-existent address?

Having this information would allow developers to implement proper error handling and avoid unnecessary API calls. For instance, if we knew the exact error response for an invalid Bitcoin address, we could perform a local validation before making an API request, thus reducing unnecessary load on your servers.

As an example of how this could be useful, my use case involves verifying payments, with an expected volume of around 50 calls per month. Knowing how to properly validate addresses and handle potential errors would help me use your API more efficiently.

Thank you for considering this request. Any additional documentation on these aspects would greatly benefit the developer community using your API.

## Summary

- **Request**: Documentation on API usage limits and error responses
- **Key Points**:
- Rate limits and usage quotas
- Possible error responses for different endpoints
- Specific errors for invalid addresses in `/address/:address` endpoint
- **Use Case**: Payment verification (~50 calls/month)
- **Benefit**: Improved error handling and API efficiency for developers