docs: added virtual environment setup process (microsoft#249)

* docs: added virtual environment setup process

* Update website/docs/Installation.md

---------

Co-authored-by: Li Jiang <bnujli@gmail.com>
Co-authored-by: Chi Wang <wang.chi@microsoft.com>

website/docs/Installation.md

@@ -1,5 +1,14 @@
 # Installation
 
+## Setup Virtual Environment
+
+When not using a docker container, we recommend using a virtual environment to install AutoGen. This will ensure that the dependencies for AutoGen are isolated from the rest of your system.
+
+```bash
+python3 -m venv autogen
+source autogen/bin/activate
+```
+
 ## Python
 
 AutoGen requires **Python version >= 3.8**. It can be installed from pip: