chore: refine doc string of global_instruction

PiperOrigin-RevId: 769650108

Author: seanzhougoogle

src/google/adk/agents/llm_agent.py

@@ -129,7 +129,7 @@ class LlmAgent(BaseAgent):
   global_instruction: Union[str, InstructionProvider] = ''
   """Instructions for all the agents in the entire agent tree.
 
-  global_instruction ONLY takes effect in root agent.
+  ONLY the global_instruction in root agent will take effect.
 
   For example: use global_instruction to make all agents have a stable identity
   or personality.
@@ -204,6 +204,11 @@ class LlmAgent(BaseAgent):
   """
   # Advance features - End
 
+  # TODO: remove below fields after migration. - Start
+  # These fields are added back for easier migration.
+  examples: Optional[ExamplesUnion] = None
+  # TODO: remove above fields after migration. - End
+
   # Callbacks - Start
   before_model_callback: Optional[BeforeModelCallback] = None
   """Callback or list of callbacks to be called before calling the LLM.