Certificate chain articles

Here's a list of articles we need to provide

- [x] What is an certificate chain?
- [ ] What is an Root certificate?
- [ ] What is an intermediate certificate?
- [ ] Root & Intermediate Certificate Bundles
- [ ] Difference between Root Certificate, Intermediate Certificate and SSL Certificate

We also need to include some specific detail about creating the appropriate Comodo bundle (#31).
Github doesn't render the numbering and headers properly, but I suspect Nanoc does this right. Just seemed worth mentioning in case there's something to investigate.