Specify python version to be < 3.8

[ghimireadarsh]

Since the tensorflow 1 doesn't have support with python 3.8, so I am raising this issue so that in documentation it can be specified to use the python < 3.8, so that people don't face issue regarding installation of libraries.

Interested @ghimireadarsh sir! Assign it to me.

[amanptl]

Check Pull Request #8.