Link to Demo 1 and 2 in the website and docs

[dlebauer]

PR #3577 tests that the notebooks compile.

Next steps:

1. add a line like this to the website but for v1.9.0
   https://github.com/PecanProject/PecanProject.github.io/blob/cfacaf2003b21b09068c495bd692dbb45d7bad6c/src/pages/tutorials.js#L14-L19
   • extra credit: move old tutorials to end of page under video, with a heading like "tutorials from previous releases"
2. Make sure that links to Demo1 and Demo2 are updated
   • https://github.com/search?q=repo%3APecanProject%2Fpecan+Demo01&type=code
   • https://github.com/search?q=repo%3APecanProject%2Fpecan+Demo02&type=code

Originally posted by @dlebauer in #3577 (comment)

[AritraDey-Dev]

I would prefer to keep this on hold until Demo2 is merged; after that, we can add those links.

[AritraDey-Dev]

Created PR here PecanProject/PecanProject.github.io#128 since we now have proper docs and both notebooks merged in the repo.