Update instruction

Author: ekzhu

python/packages/autogen-core/docs/src/user-guide/agentchat-user-guide/quickstart.md

@@ -29,6 +29,9 @@ The following example illustrates creating a simple agent team with two agents t
 1. `CodingAssistantAgent` that generates responses using an LLM model.
 2. `CodeExecutorAgent` that executes code snippets and returns the output.
 
+Because the `CodeExecutorAgent` uses a Docker command-line code executor to execute code snippets,
+you need to have [Docker installed](https://docs.docker.com/engine/install/) and running on your machine.
+
 The task is to "Create a plot of NVIDIA and TESLA stock returns YTD from 2024-01-01 and save it to 'nvidia_tesla_2024_ytd.png'."
 
 ```{include} stocksnippet.md