fix langgraph python examples readme to support platform and fastapi

Author: maxkorp

typescript-sdk/integrations/langgraph/examples/python/README.md

@@ -4,5 +4,16 @@
 
 First, make sure to create a new .env file from the .env.example and include the required keys.
 
-For python, run:
-`pnpx @langchain/langgraph-cli@latest dev`
+To run the Python examples for langgraph platform, run:
+```
+cd typescript-sdk/integrations/langgraph/examples/python
+pnpx @langchain/langgraph-cli@latest dev
+```
+
+To run the python examples using FastAPI, run:
+```
+cd typescript-sdk/integrations/langgraph/examples/python
+poetry install
+poetry run dev
+```
+