docs: Update README to reflect torch 2 support

Update the README file to remove the "experimental" tag from the documentaion.

The existance of the tag was an oversight as Torch 2.x has been supported for 18+ months at this point.

Additionally, clean-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