Document response headers for rate limiting

[ThisIsMissEm]

Added response headers for rate limiting middleware.

Note: these headers are not the same as the proposed internet draft for rate limiting: https://www.ietf.org/archive/id/draft-ietf-httpapi-ratelimit-headers-10.html

❓ Type of change

• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

I couldn't find this information in the documentation, so decided to add it.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[thetutlage]

Thanks 👍🏽