## PR title
partners: changed the README file for the Fireworks integration in the
libs/partners/fireworks folder
## PR message
Description: Changed the README file of partners/fireworks following the
docs on https://python.langchain.com/docs/integrations/llms/Fireworks
The README includes:
- Brief description
- Installation
- Setting-up instructions (API key, model id, ...)
- Basic usage
Issue: https://github.com/langchain-ai/langchain/issues/17545
Dependencies: None
Twitter handle: None
