Add National Science Foundation to TOC

[reginankenchor]

This PR updates the TOC file to include NSF under organizations, following the addition made in PR #136.

[RichardLitt]

Thanks, @reginankenchor. I think this should be in #136, as it relies upon the work there, and as it shouldn't be considered it's own piece of work. For instance, if I merged this, it would be a dead link until I also merged #136. And #136 shouldn't be merged until the code in here is part of it. So, ideally, this would just be part of that PR. Does that make sense?

I could merge both of these together, but I am hoping to have you learn about how software development works in the process.

[reginankenchor]

Thanks, @reginankenchor. I think this should be in #136, as it relies upon the work there, and as it shouldn't be considered it's own piece of work. For instance, if I merged this, it would be a dead link until I also merged #136. And #136 shouldn't be merged until the code in here is part of it. So, ideally, this would just be part of that PR. Does that make sense?

I could merge both of these together, but I am hoping to have you learn about how software development works in the process.

Thank you @RichardLitt Yes I understand. Thank you. Going forward I will merge them together.