Update Aeon environment set-up instructions

[anayapouget]

In the option 2 set-up instructions using pip and venv:

• The python version required for installation should be changed from ">=3.9" to ">=3.11".
• The env activation code source aeon/bin/activate works on linux but not on windows, so instructions could be updated for other OS

This won't really be relevant in the future but for now we may also want to note that if you follow the option 1 set-up instructions using conda, you also have to run pip install -e . for the aeon module to be recognized.