Update FAQ.md, elaborate on how to customise docker image and pick 'p…

…ython:3' to solve typical errors (#269)

* Update FAQ.md

* Update website/docs/FAQ.md

Co-authored-by: Qingyun Wu <qingyun.wu@psu.edu>

* Update website/docs/FAQ.md

Co-authored-by: Qingyun Wu <qingyun.wu@psu.edu>

* Update website/docs/FAQ.md

Co-authored-by: Qingyun Wu <qingyun.wu@psu.edu>

---------

Co-authored-by: Qingyun Wu <qingyun.wu@psu.edu>

website/docs/FAQ.md

@@ -141,3 +141,20 @@ We strongly recommend using docker to execute code. There are two ways to use do
 
 1. Run autogen in a docker container. For example, when developing in GitHub codespace, the autogen runs in a docker container.
 2. Run autogen outside of a docker, while perform code execution with a docker container. For this option, make sure the python package `docker` is installed. When it is not installed and `use_docker` is omitted in `code_execution_config`, the code will be executed locally (this behavior is subject to change in future).
+
+### Enable Python 3 docker image
+
+You might want to override the default docker image used for code execution. To do that set `use_docker` key of `code_execution_config` property to the name of the image. E.g.:
+```python
+user_proxy = autogen.UserProxyAgent(
+    name="agent",
+    human_input_mode="TERMINATE",
+    max_consecutive_auto_reply=10,
+    code_execution_config={"work_dir":"_output", "use_docker":"python:3"},
+    llm_config=llm_config,
+    system_message=""""Reply TERMINATE if the task has been solved at full satisfaction.
+Otherwise, reply CONTINUE, or the reason why the task is not solved yet."""
+)
+```
+
+If you have problems with agents running `pip install` or get errors similar to `Error while fetching server API version: ('Connection aborted.', FileNotFoundError(2, 'No such file or directory')`, you can choose **'python:3'** as image as shown in the code example above and that should solve the problem.