Elijah Hopp

I made a striped fork of fmt named fmt-headeronly. I think it applies: https://github.com/MrZeusTheCoder/fmt-headeronly

The link to the NCC Group Whitepaper "Assessing Unikernel Security" seems to have moved from `https://research.nccgroup.com/wp-content/uploads/2020/07/ncc_group-assessing_unikernel_security.pdf` to `https://www.nccgroup.com/media/tgsj1css/_ncc_group-assessing_unikernel_security.pdf`. This PR would fix all (only one, actually) occurrences of the broken...

With the shift to the app catalog, the Baby Steps page got left behind. This PR instead links readers to the [catalog repo](https://github.com/unikraft/catalog) and the [Using the Application Catalog](https://unikraft.org/guides/using-the-app-catalog) page....