Fix typo on Agent documentation (openai#151)

Argument name is not description but handoff_description

Author: rm-openai

src/agents/agent.py

@@ -27,8 +27,8 @@ class Agent(Generic[TContext]):
     """An agent is an AI model configured with instructions, tools, guardrails, handoffs and more.
 
     We strongly recommend passing `instructions`, which is the "system prompt" for the agent. In
-    addition, you can pass `description`, which is a human-readable description of the agent, used
-    when the agent is used inside tools/handoffs.
+    addition, you can pass `handoff_description`, which is a human-readable description of the
+    agent, used when the agent is used inside tools/handoffs.
 
     Agents are generic on the context type. The context is a (mutable) object you create. It is
     passed to tool functions, handoffs, guardrails, etc.