Fix Burgers, Navier Stokes Demo

[clarencew0083]

1. Language editing/proofreading/fact-checking

2. To run the cells so that they have the results displayed

3. Add 'Open in Colab' button e.g., https://github.com/stephenbaek/padl/blob/main/labs/01_introduction_to_pytorch.ipynb

4. Burgers - Cell 5: Reynolds number should be scalar and not be displayed.

5. Burgers - Cell 7: Remove the comments (4 lines) at the beginning

6. the default value for weights_only will be flipped to True.