docs: simplify openapi spec update instructions in CONTRIBUTING.md

The spec update is now automated via PR from the langfuse repo.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: wochinge

CONTRIBUTING.md

@@ -45,9 +45,7 @@ uv run mypy langfuse --no-error-summary
 
 ### Update openapi spec
 
-1. Generate Fern Python SDK in [langfuse](https://github.com/langfuse/langfuse) and copy the files generated in `generated/python` into the `langfuse/api` folder in this repo.
-2. Execute the linter by running `uv run ruff format .`
-3. Rebuild and deploy the package to PyPi.
+A PR with the changes is automatically created upon changing the Spec in the langfuse repo.
 
 ### Publish release