Add requirements.txt

• Allows simplifying local setup instructions without docker.
• Also use python venv (which is builtin with standard python3).
• Install as much stuff to python venv as possible to make things more cross-plaform.
• Fix some minor bash snippets which were not labled (and thus were being treated as cpp snippets)

Signed-off-by: Ayush Singh ayushdevel1325@gmail.com