Broken Links: contributions Link + other content links

[williamctburke]

Broken Links
https://m2n037.github.io/master/contributions.md doesn't currently work.
https://ntrs.nasa.gov/404?original=%2Fsearch.jsp
https://encyclopedia.che.engin.umich.edu/Pages/PolymerProcessing/menu.html

Also,
Hi Mukunda! My name is William Burke and I write a bunch of engineering educational content at Five Flute. We have an engineering guide that I think would be a great addition to your list. Are you up for including it? Let me know your thoughts!