Fix limiter README to reflect algorithm used

[bbangert]

The README for the limiter says:

This module provides an interface for token bucket rate limiting with precise control over limits and time windows. Inspired by GitHub's approach to scaling their API with a sharded, replicated rate limiter in Valkey (github.blog).

However, the blog post and the implementation are actually using a fixed window approach, not a token bucket.

[rueian]

Hi @bbangert, would you like to help us fix the README?

[bbangert]

Sure, its #64

[rueian]

Thanks for the fix @bbangert