docs: Improve README

Update the README file to improve readability, clarity, and markdown formatting standards.

Cleaned up and improvements were applied to the document:

- Correctly indented content within bullet-point lists.
- Used GitHub flavored markdown to enable NOTE, TIP, etc. callouts where appropriate.
- Reflowed text to use the more standard new-line after every sentance style.
- Replaced works this "this", "here", and "link" with more descriptive terms for link text.
- Corrected the format of the pbtxt examples.
- Updated the recommended pytorch container from NGC.

Author: whoisj