Help wanted: add support for categories to the blog

[brianwarner]

I'm opening this issue as a placeholder, in case someone has some spare cycles and is looking for a way they can help out with the website.

I recently pushed a bunch of new content during the migration from https://foundation.graphql.org to https://graphql.org/foundation. This included quite a few news items, which ended up in a flat list on https://graphql.org/blog/

I added tags to the front matter of each post, and I also found instructions on adding tags to blog posts. However, our installation has been customized and the instructions don't quite align with our site. This was my first go with Gatsby, and I wasn't able to get it working. I'm hoping that someone who is a little more familiar with Gatsby and React might do better at implementing nice-looking tag pages than I did.

So, I'm opening this as a "help requested" issue. If you're interested in giving it a shot, please feel free to jump in!