docs: fix shell command with escaped brackets in pip install (#6464)

Fix the installation command in
`python/samples/agentchat_chainlit/README.md` by properly escaping or
quoting package names with square brackets to prevent shell
interpretation errors in zsh and other shells.

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## Why are these changes needed?

[AS-IS]

![image](https://github.com/user-attachments/assets/d6c8c95a-eb45-4206-a147-cd74aa6e949f)

[After fixed]

![image](https://github.com/user-attachments/assets/f2ffea4b-f993-4888-8559-c19e2b5c6eea)


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## Related issue number

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Co-authored-by: Victor Dibia <victordibia@microsoft.com>

python/samples/agentchat_chainlit/README.md

@@ -10,7 +10,7 @@ and support streaming messages.
 To run this sample, you will need to install the following packages:
 
 ```shell
-pip install -U chainlit autogen-agentchat autogen-ext[openai] pyyaml
+pip install -U chainlit autogen-agentchat "autogen-ext[openai]" pyyaml
 ```
 
 To use other model providers, you will need to install a different extra