Update README.md

[dbennerIBM]

missing role parameter in the client.py example in README.md, this fixes an error where the current code cannot talk to agent.py server.

[pilartomas]

Hello, are you sure this is the culprit? Pydantic should apply user as the default role when it is not specified:

acp/python/src/acp_sdk/models/models.py

Line 169 in c0f4b8c

role: Literal["user"] | Literal["agent"] | str = Field("user", pattern=r"^(user|agent(\/[a-zA-Z0-9_\-]+)?)$")

Regardless, we should merge this to make the example more explicit 👍