Add Run Target To Makefile And Implement Main Script

[sanjeevz3009]

What is the context of this PR?

Addresses the issue raised by @delterr, #69.

Currently in the project template README.md we have the instruction below, which unfortunately doesn't do anything when followed. This PR fixes this issue by adding a run target in the project template Makefile and to reflect the change adding a main python script which utilises calculator.py.

3. Run the application
make run   

How to review

• Pull down the branch/ latest changes
• Generate a new python template repo -> make run -> the script should work as expected (you will see the output from the python script that's being executed)
• Make sure to test with Poetry and Pipenv

Follow-up Actions

List any follow-up actions (if applicable), like needed documentation updates or additional testing.