docs: Add Agent Engine with ADK examples to README.

PiperOrigin-RevId: 808750306

Author: yeesian

README.rst

@@ -97,6 +97,79 @@ Then run evaluation by providing the inference results and specifying the metric
  ]
  )
 
+Agent Engine with Agent Development Kit (ADK)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+First, define a function that looks up the exchange rate:
+
+.. code-block:: Python
+
+ def get_exchange_rate(
+ currency_from: str = "USD",
+ currency_to: str = "EUR",
+ currency_date: str = "latest",
+ ):
+ """Retrieves the exchange rate between two currencies on a specified date.
+
+ Uses the Frankfurter API (https://api.frankfurter.app/) to obtain
+ exchange rate data.
+
+ Returns:
+ dict: A dictionary containing the exchange rate information.
+ Example: {"amount": 1.0, "base": "USD", "date": "2023-11-24",
+ "rates": {"EUR": 0.95534}}
+ """
+ import requests
+ response = requests.get(
+ f"https://api.frankfurter.app/{currency_date}",
+ params={"from": currency_from, "to": currency_to},
+ )
+ return response.json()
+
+Next, define an ADK Agent:
+
+.. code-block:: Python
+
+ from google.adk.agents import Agent
+ from vertexai.agent_engines import AdkApp
+
+ app = AdkApp(agent=Agent(
+ model="gemini-2.0-flash", # Required.
+ name='currency_exchange_agent', # Required.
+ tools=[get_exchange_rate], # Optional.
+ ))
+
+Test the agent locally using US dollars and Swedish Krona:
+
+.. code-block:: Python
+
+ async for event in app.async_stream_query(
+ user_id="user-id",
+ message="What is the exchange rate from US dollars to SEK today?",
+ ):
+ print(event)
+
+To deploy the agent to Agent Engine:
+
+.. code-block:: Python
+
+ remote_app = client.agent_engines.create(
+ agent=app,
+ config={
+ "requirements": ["google-cloud-aiplatform[agent_engines,adk]"],
+ },
+ )
+
+You can also run queries against the deployed agent:
+
+.. code-block:: Python
+
+ async for event in remote_app.async_stream_query(
+ user_id="user-id",
+ message="What is the exchange rate from US dollars to SEK today?",
+ ):
+ print(event)
+
 Prompt optimization
 ^^^^^^^^^^^^^^^^^^^