text: Title: Add more explicit steps to the Getting Started example
  Body: Improve the [Getting Started section of the docs](https://testbook.readthedocs.io/en/latest/getting-started/index.html#create-your-first-test).
  
  Right now it's easy to miss that two files are needed: a notebook (`.ipynb` file) to test and a test file (`.py` file) to write the tests.
  
  It would also be helpful to add an explicit step on how to run the test file.