Remove --no-site-packages flag from virtualenv command and update the supported python version. (#8551)

* Remove --no-site-packages flag from virtualenv.

* change python version to least supported version.

---------

Co-authored-by: Matthew Soulanille <msoulanille@google.com>

Author: shmishra99

tfjs-converter/README.md

@@ -26,22 +26,22 @@ __0. Please make sure that you run in a Docker container or a virtual environmen
 
 __Note__: *Check that [`tf-nightly-cpu-2.0-preview`](https://pypi.org/project/tf-nightly-cpu-2.0-preview/#files) is available for your platform.*
 
-Most of the times, this means that you have to use Python 3.6.8 in your local
-environment. To force Python 3.6.8 in your local project, you can install
+Most of the times, this means that you have to use Python 3.7.10 in your local
+environment. To force Python 3.7.10 in your local project, you can install
 [`pyenv`](https://github.com/pyenv/pyenv) and proceed as follows in the target
 directory:
 
 ```bash
-pyenv install 3.6.8
-pyenv local 3.6.8
+pyenv install 3.7.10
+pyenv local 3.7.10
 ```
 
 Now, you can
 [create and activate](https://packaging.python.org/guides/installing-using-pip-and-virtual-environments/)
 a `venv` virtual environment in your current folder:
 
 ```bash
-virtualenv --no-site-packages venv
+virtualenv venv
 . venv/bin/activate
 ```