Updates readme to use consistent python3 version

[Hamma111]

The same python version should be consistently used. Right now, we could be using a different python version to set up the venv but another python to install requirements and running the scripts.

While this is an uncommon scenario, but still might be relevant for a lot of scenarios.

Breakdown of the issue:

1. Virtual Env was being created using python3 but all the subsequent commands utilize the python
2. In most cases, python and python3 could be referencing to different python versions.
3. We should be using the same python command we created the venv with i.e. python3

[Stephanvs]

looks good to me